Tutorial: Simple Connection

[vector-of-bool]

This adds a very basic tutorial for connecting to a server, distinct from the more complex "communicating" how-to page.

This also adds several convenience APIs that make code much easier to read/write:

• Overloads for amongoc_{then,let,just} for common parameter sets.
• Test cases to ensure that the "overload" function macros are invocable in both C and C++ (this caught a few issues).
• amongoc_detach_start for when you don't care about the operation state storage.

[kevinAlbs]

LGTM with tracing disabled. Not needed in this PR, but I request adding an example to show a CRUD operation (insert/find), which I expect most users would want to try.

[kevinAlbs]

Suggest disabling the default enabled tracing. This example currently prints the full OPMSG sent and received:

send OP_MSG #0 (135 bytes)
  Section #1 body: {
    "hello": 1:i32,
    "$db": "admin",
    "client": {
      "driver": {
        "name": "amongoc",
        "version": "experimental-dev",
      },
      "os": { "type": "Linux" },
    },
  }

[vector-of-bool]

Not sure how that got in. Oop.