This reverts commit 3420a145, reversing
changes made to afb66a5a.

Users should never publicly be interacting with an instance of this.  The instance that comes along with an `AC::Connection::Base` instance (the only thing a user should be working with) is [itself intended to be private](https://github.com/tjschuck/rails/blob/master/actioncable/lib/action_cable/connection/base.rb#L137-L140).

[ci skip]

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

This is primarily for backwards compatibility for when
or if the protocol is changed in future versions.

If the server fails to respond with an acceptable
protocol, the client disconnects and disables
the monitor.

(as adapted to use concurrent-ruby / nio4r instead of eventmachine)

Warnings coming from code and test are removed

* Move specific requires close to where they're needed.
* Use the private active_support/rails dep to wrap up common needs
  like eager autoload and module delegation.
* Use a single Rails engine rather than an engine and a railtie.
* Prefer `AS::JSON.encode` to `Object#to_json`.