Implement code/test for `last`
Add code/test to protect against negative index.

Add test for short selectors.
Add dom constants and configuration
Implement code for `add` and `matches` WIP
Move `Selector.prototype.less` to `Selector.tail`.
Move stuff to CONSTANTS
More statics (local).

Slice instead of storing `arguments`
Rearange code and add more comments
Ensure candidates are returned in the order they were added.
Added some more tests, we should really add more.
Make sure to use UNIVERSAL
Add headers to source files.
Fix Opera bug when SVGAnimatedString is not exposed.

See https://github.com/josh/selector-set/commit/69dcd66280d61741c237e002f5b333a7744cfe15
Merge pull request #45 from troopjs/feature/selector

Port part of selector-set to component/widget