ES2015 EventEmitter3

This is a direct port of EventEmitter3 to es2015. It passes the tests exactly (see Caveats below).

This aims to be a drop in replacement for 99% of use cases.

Caveats

Because we are now using a class instead of a prototype, util.inherits now does not work. If you find a solution to this, please file a pull request.

Similarly because we are now exporting a class, the exported object is slightly different. It now does not contain proxies for EventEmitter2 and EventEmitter3.

TODO

allow usage with npm, bower, and component.