Add github action for merging main branch

The main branch was renamed from master to main, the workflow will merge
changes across to master for now in case there are forks which use
master.

Also update CI badge

Removes some old dependency files, now that Go modules are used by all supported versions.

Also removes appveyor CI. Either CircleCI or github actions would do for
windows builds.

.github/workflows/sync-main.yaml

@@ -0,0 +1,18 @@
+name: Merge main into master
+
+on:
+  push:
+    branches: [main]
+
+jobs:
+  sync:
+    name: Merge main branch
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with: {fetch-depth: 0}
+    - name: merge
+      run: |
+        git checkout master
+        git merge --ff-only main
+        git push origin master

CONTRIBUTING.md

@@ -10,21 +10,3 @@ explaining the feature and why it is necessary.
 
 Pull requests for bug fixes are always appreciated. They should almost always
 include a test which fails without the bug fix.
-
-## Dependencies
-
-At this time both a `Gopkg.toml` for `dep` and `go.mod` for go modules exist in
-the repo. The `Gopkg.toml` remains so that projects using earlier versions of Go
-are able to find compatible versions of dependencies.
-
-If you need to make a change to a dependency:
-
-1. Update `Gopkg.toml`.
-2. Run the following to sync the changes to `go.mod`.
-   ```
-   dep ensure
-   rm go.mod go.sum
-   go mod init
-   gotestsum
-   go mod tidy
-   ```

README.md

@@ -3,7 +3,7 @@
 A collection of packages to augment `testing` and support common patterns.
 
 [![GoDoc](https://godoc.org/gotest.tools?status.svg)](https://pkg.go.dev/gotest.tools/v3/?tab=subdirectories)
-[![CircleCI](https://circleci.com/gh/gotestyourself/gotest.tools/tree/master.svg?style=shield)](https://circleci.com/gh/gotestyourself/gotest.tools/tree/master)
+[![CircleCI](https://circleci.com/gh/gotestyourself/gotest.tools/tree/main.svg?style=shield)](https://circleci.com/gh/gotestyourself/gotest.tools/tree/main)
 [![Go Reportcard](https://goreportcard.com/badge/gotest.tools)](https://goreportcard.com/report/gotest.tools)
 
 ## Usage