Remove coffee files from gitignore. Corrections to the readme.md

Updated the bbb-webhooks documentation. Ensuring the configuration file gets ignored.

The way the checksum is calculated now is more similar to the other API calls,
specially setConfigXML. It uses the content type 'application/x-www-form-urlencoded'
so the information in the post body doesn't have to be converted from/to
js/string, preventing possible checksum errors in different programming
languages.

Started using coffee-script, updated the libraries, and now it subscribes
to all channels under 'bigbluebutton:*' so we can receive all events that
happened and select the ones we want.