Added gulpfile.js into .npmignore
Added the "scope" parameter to the #on method

This parameter makes it possible to add an object that will be the scope of the handler when a related event is dispatched.
Added doc for "scope" option in #on documentation
Improved #once to allow other options

The #once method now can take its own options object (which is still optional), and will override the "once" value to true.
Also added related unit tests.
Release v2.1.0

 - Improved #once that now accepts other options
 - Added the "scope" option to force handlers scope