use correct filename in example

closes #80

.js.coffee -> .coffee

 It was initially required, but support for the shorthand has been
 supported since sprockets 2.1. Eventually 4.x will only support the
 shorthand version. Just want to get new people using the prefer stuff
 ASAP.

Support connection identifiers that don't implement to_global_id

Remove out-of-date AC::Broadcaster reference

Remove out-of-data autoload reference of ActionCable::Broadcaster that removed at e1a99a83 .

Clear out the streams when they are stopped.

Update README.md

Move require of to_param to where it is needed

update docs for broadcast_to to pass a message.

Fixes test failure in ActionCable::Channel::BroadcastingTest when run by itself

Fixing documentation, correcting grammar, and removing unnecessary whitespace

Optimize channel class lookup

refactor channel look up to use a hash instead of an array and reduce the number of calls to safe_constantize because it can be slow

Run tests with Travis.

add broadcast_to and stream_for methods as per #26

Move VERSION constant to version file and use this in the gemspec