ES6 documentation

[PEM--]

See #52

[astorije]

Hey @PEM--, thank you very much for this!
Note that changes to the README should come along with the respective code comment. For example, .empty's doc in the README matches this comment in the code.

At this point, this should be tied to #74, which is one of the 2 things that will trigger the v2 of this plugin.

I'll ping you when I start porting this repo to ES6.

[PEM--]

Hi @astorije. Thanks for this nice addition to my test suite. For easing the port to ES6, you should definitely have a look at: http://lebab.io/ 😉

[astorije]

Hey @PEM--, sorry for the long, loooong delay. Would you mind rebasing on master and fixing conflicts please? :)

[astorije]

Closing this as I expect #142 will supersede it. Thanks for your help @PEM--!!