ES6 support

[jfirebaugh]

Currently blocked by lack of parser support: http://esprima.org/doc/es6.html

Running list of things to support:

• [x] Switch to espree

• [ ] JSDocs in destructuring assignment:

  { /** docs */ a, /** docs */ b } = { ... }

[tmcw]

Looks like espree does this better and doesn't break from the AST tradition like babel does

[mourner]

+1 for Espree http://eslint.org/blog/2014/12/espree-esprima/

[tmcw]

This will be actionable once #732 is merged, and I'll write a thorough summary for help wanted.

[tmcw]

I first dove in on trying to solve

function a(b /** this would have docs in it */) {}

But this is unfortunately tricky. We prefer to parse comments as leadingComments first, and that comment is a leading comment for the function body as well as a trailing comment for the param a.

Destructuring patterns don't have this problem. Looking into them.