Support ES2015 natively

[eddiemonge]

It'd be nice to see support for ES2015 without having to first transpile it to ES5 code. As more browsers support ES2015, I think we will see a declining need for the transpiler step so it'd be good to see this support it as well.

[olov]

I won't be able to donate the time needed for supporting this and I'm not very fond of adding additional complexity to ng-annotate. If someone steps up to write and maintain the needed code, I'll be happy to merge a PR.

[olov]

#245

[schmod]

This is very specifically being addressed in #245, so please head over there if you're interested.