Phoenix: Publish API documentation for the Phoenix Channels JavaScript client

[ericlathrop]

The only documentation for the JavaScript side that I could find was in the guides. The guide is nice, but
comprehensive API documentation should be published for reference.

[chrismccord]

This is something that I'd like to get out once we extract the client to its own repo (current WIP), for now the source is your best bet https://github.com/phoenixframework/phoenix/blob/master/web/static/js/phoenix.js#L1-L86

Thanks for the idea!

[bchase]

For anyone else who stumbles across this, master now uses the new v1.3 file structure, so phoenix.js has moved here:

https://github.com/phoenixframework/phoenix/blob/master/assets/js/phoenix.js#L2-L103

[michalmuskala]

In the next release they also should be generated as part of regular documentation thanks to https://github.com/phoenixframework/phoenix/pull/2333