Provide first batch of scaler documentation (kedacore#4)

* Provide first batch of scaler documentation

* Add caveat for Azure EH

content/scalers/apache-kafka-topic.md

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+fragment = "content"
+weight = 100
+title = "Apache Kafka Topic"
+background = "light"
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+
+Scale applications based on Apache Kafka Topic.
+
+**Availability:** v1.0+ | **Maintainer:** Community
+
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `kafka` trigger for Apache Kafka Topic.
+
+```yaml
+  triggers:
+  - type: kafka
+    metadata:
+      brokerList: kafka.svc:9092
+      consumerGroup: my-group
+      topic: test-topic
+      lagThreshold: '5' # Optional. How much the stream is lagging on the current consumer group
+```
+
+### Authentication Parameters
+
+Not supported yet.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: kafka-scaledobject
+  namespace: default
+  labels:
+    deploymentName: azure-functions-deployment
+spec:
+  scaleTargetRef:
+    deploymentName: azure-functions-deployment
+  pollingInterval: 30
+  triggers:
+  - type: kafka
+    metadata:
+      # Required
+      brokerList: localhost:9092
+      consumerGroup: my-group       # Make sure that this consumer group name is the same one as the one that is consuming topics
+      topic: test-topic
+      lagThreshold: "50"
+```

content/scalers/aws-cloudwatch.md

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+fragment = "content"
+weight = 100
+title = "AWS Cloudwatch"
+background = "light"
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+
+Scale applications based on a AWS Cloudwatch.
+
+**Availability:** v1.0+ | **Maintainer:** Community
+
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `aws-cloudwatch` trigger that scales based on a AWS Cloudatch.
+
+```yaml
+triggers:
+  - type: aws-cloudwatch
+    metadata:
+      # Required: namespace
+      namespace: AWS/SQS
+      # Required: Dimension Name
+      dimensionName: QueueName
+      dimensionValue: keda
+      metricName: ApproximateNumberOfMessagesVisible
+      targetMetricValue: "2"
+      minMetricValue: "0"
+      # Required: region
+      awsRegion: "eu-west-1"
+      # Optional: AWS Access Key ID
+      awsAccessKeyID: AWS_ACCESS_KEY_ID # default AWS_ACCESS_KEY_ID
+      # Optional: AWS Secret Access Key
+      awsSecretAccessKey: AWS_SECRET_ACCESS_KEY # default AWS_SECRET_ACCESS_KEY
+```
+
+### Authentication Parameters
+
+Not supported yet.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: aws-cloudwatch-queue-scaledobject
+  namespace: keda-test
+  labels:
+    deploymentName: nginx-deployment
+    test: nginx-deployment
+spec:
+  scaleTargetRef:
+    deploymentName: nginx-deployment
+  triggers:
+  - type: aws-cloudwatch
+    metadata:
+      namespace: AWS/SQS
+      dimensionName: QueueName
+      dimensionValue: keda
+      metricName: ApproximateNumberOfMessagesVisible
+      targetMetricValue: "2"
+      minMetricValue: "0"
+      awsRegion: "eu-west-1"
+      awsAccessKeyID: AWS_ACCESS_KEY_ID
+      awsSecretAccessKey: AWS_SECRET_ACCESS_KEY
+```

content/scalers/aws-sqs.md

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+fragment = "content"
+weight = 100
+title = "AWS SQS Queue"
+background = "light"
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+
+Scale applications based on AWS SQS Queue.
+
+**Availability:** v1.0+ | **Maintainer:** Community
+
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `aws-sqs-queue` trigger for AWS SQS Queue.
+
+```yaml
+triggers:
+  - type: aws-sqs-queue
+    metadata:
+      # Required: queueURL
+      queueURL: https://sqs.eu-west-1.amazonaws.com/<acccount_id>/testQueue
+      # Optional: region
+      awsRegion: "eu-west-1"
+      # Optional: AWS Access Key ID
+      awsAccessKeyID: AWS_ACCESS_KEY_ID_ENV_VAR # default AWS_ACCESS_KEY_ID
+      # Optional: AWS Secret Access Key
+      awsSecretAccessKey: AWS_SECRET_ACCESS_KEY_ENV_VAR # default AWS_SECRET_ACCESS_KEY
+      # Optional
+      queueLength: "5" # default 5
+```
+
+### Authentication Parameters
+
+Not supported yet.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: aws-sqs-queue-scaledobject
+  namespace: default
+  labels:
+    deploymentName: nginx-deployment
+    test: nginx-deployment
+spec:
+  scaleTargetRef:
+    deploymentName: nginx-deployment
+  triggers:
+  - type: aws-sqs-queue
+    metadata:
+      queueURL: https://sqs.eu-west-1.amazonaws.com/<acccount_id>/testQueue
+      awsRegion: "eu-west-1"
+      awsAccessKeyID: AWS_ACCESS_KEY_ID_ENV_VAR
+      awsSecretAccessKey: AWS_SECRET_ACCESS_KEY_ENV_VAR
+      queueLength: "5"
+```

content/scalers/azure-event-hub.md

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+fragment = "content"
+weight = 100
+title = "Azure Event Hubs"
+background = "light"
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+
+Scale applications based on Azure Event Hubs†.
+
+**Availability:** v1.0+ | **Maintainer:** Microsoft
+
+<!--more-->
+
+_†: As of now, the Event Hub scaler only supports reading from Blob Storage, as well as scaling only Event Hub applications written in C#, Python or created with Azure Functions._
+
+### Trigger Specification
+
+This specification describes the `azure-eventhub` trigger for Azure Event Hubs.
+
+```yaml
+  triggers:
+  - type: azure-eventhub
+    metadata:
+      connection: EVENTHUB_CONNECTIONSTRING_ENV_NAME # Connection string for Event Hub namespace
+      storageConnection: STORAGE_CONNECTIONSTRING_ENV_NAME # Connection string for account used to store checkpoint. As of now the Event Hub scaler only reads from Azure Blob Storage. 
+      consumerGroup: $Default # Optional. Consumer group of event hub consumer. Default: $Default
+      unprocessedEventThreshold: '64' # Optional. Target number of unprocessed events across all partitions in Event Hub for HPA. Default: 64 events.
+```
+
+The `connection` value is the name of the environment variable your deployment uses to get the Event Hub connection string. `storageConnection` is the name of the environment variable your deployment uses to get the Storage connection string.
+
+Environment variables are usually resolved from a `Secret V1` or a `ConfigMap V1` collections. `env` and `envFrom` are both supported.
+
+### Authentication Parameters
+
+Not supported yet.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: azure-eventhub-scaledobject
+  namespace: default
+  labels:
+    deploymentName: azureeventhub-function
+spec:
+  scaleTargetRef:
+    deploymentName: azureeventhub-function
+  triggers:
+  - type: azure-eventhub
+    metadata:
+      # Required
+      connection: EventHub
+      storageConnection: AzureWebJobsStorage
+      # Optional
+      consumerGroup: $Default # default: $Default
+      unprocessedEventThreshold: '64' # default 64 events.
+```

content/scalers/azure-service-bus.md

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 Scale applications based on Azure Service Bus Queues or Topics.
 
-**Availability:** v1.0 and above | **Maintainer:** Microsoft
+**Availability:** v1.0+ | **Maintainer:** Microsoft
 
-<!--more-->
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `azure-servicebus` trigger for Azure Service Bus Queue or Topic.
+
+```yaml
+  triggers:
+  - type: azure-servicebus
+    metadata:
+      # Required: queueName OR topicName and subscriptionName
+      queueName: functions-sbqueue
+      # or
+      topicName: functions-sbtopic
+      subscriptionName: sbtopic-sub1
+      # Required
+      connection: SERVICEBUS_CONNECTIONSTRING_ENV_NAME # This must be a connection string for a queue itself, and not a namespace level (e.g. RootAccessPolicy) connection string [#215](https://github.com/kedacore/keda/issues/215)
+      # Optional
+      queueLength: "5" # Optional. Subscription length target for HPA. Default: 5 messages
+```
+
+The `connection` value is the name of the environment variable your deployment uses to get the connection string. This is usually resolved from a `Secret V1` or a `ConfigMap V1` collections. `env` and `envFrom` are both supported.
+
+### Authentication Parameters
+
+To be documented.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: azure-servicebus-queue-scaledobject
+  namespace: default
+  labels:
+    deploymentName: azure-servicebus-queue-function
+spec:
+  scaleTargetRef:
+    deploymentName: azure-servicebus-queue-function
+  triggers:
+  - type: azure-servicebus
+    metadata:
+      # Required: queueName OR topicName and subscriptionName
+      queueName: functions-sbqueue
+      # or
+      topicName: functions-sbtopic
+      subscriptionName: sbtopic-sub1
+      # Required
+      connection: SERVICEBUS_CONNECTIONSTRING_ENV_NAME
+      # Optional
+      queueLength: "5" # default 5
+
+```

content/scalers/azure-storage-queue.md

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+fragment = "content"
+weight = 100
+title = "Azure Storage Queue"
+background = "light"
++++
+
+Scale applications based on Azure Storage Queues.
+
+**Availability:** v1.0+ | **Maintainer:** Microsoft
+
+<!--more-->
+
+### Trigger Specification
+
+This specification describes the `azure-queue` trigger for Azure Storage Queue.
+
+```yaml
+triggers:
+  - type: azure-queue
+    metadata:
+      queueName: functionsqueue
+      queueLength: '5' # Optional. Queue length target for HPA. Default: 5 messages
+      connection: STORAGE_CONNECTIONSTRING_ENV_NAME
+```
+
+The `connection` value is the name of the environment variable your deployment uses to get the connection string. This is usually resolved from a `Secret V1` or a `ConfigMap V1` collections. `env` and `envFrom` are both supported.
+
+### Authentication Parameters
+
+Not supported yet.
+
+### Example
+
+```yaml
+apiVersion: keda.k8s.io/v1alpha1
+kind: ScaledObject
+metadata:
+  name: azure-queue-scaledobject
+  namespace: default
+  labels:
+    deploymentName: azurequeue-function
+spec:
+  scaleTargetRef:
+    deploymentName: azurequeue-function
+  triggers:
+  - type: azure-queue
+    metadata:
+      # Required
+      queueName: functionsqueue
+      # Optional
+      connection: STORAGE_CONNECTIONSTRING_ENV_NAME # default AzureWebJobsStorage
+      queueLength: "5" # default 5
+```