Fix docs about `sourceFile`/`directSourceFile`.
Fix sentence broken by 11dc953bc67195d978d59d106b48f8c0606c5bc0
Split ES6 Template logic from main functionality.
Add basic ES6 support in util/walk.js
Mark version 0.7.0
Bump version number post 0.7
Make token format compatible with Esprima and Mozilla-styled locations.

* Tokens are now instances of single exported constructor Token.
* Token objects are compatible with Esprima (only `type` format is different).
* Added token.loc in format of node.loc (Mozilla).
* Deprecated token.startLoc & token.endLoc.
* Updated comment generation example.
Allow arrays in `onToken` and `onComment` for easier comment attachment.

Added ability to pass arrays in `onToken`/`onComment` where tokens/comments
will be collected in Esprima's format so you can simply pass those arrays to
`escodegen.attachComments`.

Updated docs and comment attachment example.