Add support for decorators

[winstliu]

Closes #163

/cc @mehcode

[mehcode]

Looks awesome @50Wliu

[silvenon]

👍

[winstliu]

Updated for the ES2016 syntax based on examples and terminology from https://medium.com/google-developers/exploring-es7-decorators-76ecb65fb841#.blq52cu0r.

[winstliu]

Marking as blocked until the proposal is standardized.

[icecream17]

the proposal is standardized now

[winstliu]

Thanks @icecream17, I'll see if there's any updates I need to handle from the standardized proposal and also try to resolve the merge conflicts if they're not too nasty.

[winstliu]

@icecream17 where are you seeing that the proposal is standardized? It still appears to be in Stage 2, from what I can find: https://github.com/tc39/proposals/blob/2c2ad83616b845af6c8000e367140932dd4f1c88/README.md#stage-2

[icecream17]

Oh what - I thought it was 2017. Hmm, must've got confused. Oops. Sorry about that.

Yeah you're right, still not standardized yet.