Make #root chainable, corrections to incorrect jsDoc & more

Every time I look at **dom-delegate** I find something else I want to change...

This pull request:-
- Makes `#root` chainable (for consistency with `#off` and `#on`) - includes regression tests*.
- Various updates to jsDoc.
- Tiny formatting fix in common js / window attachment for consistency with tabs and spaces.
- Bump to v0.2.1.

\* Maybe we should add tests to check `#on` and `#off` are chainable too..