Optimize player sorting.

* Sort by sequence number per spec.
* Don't require a stable sort.
* Track and invalidate the sorted state.
Implement positionListType for animating CSS property background-position
Merge pull request #360 from alancutter/positionListType

Implement positionListType for animating CSS property background-position
Merge pull request #359 from dstockwell/sort-players

Optimize player sorting.
Added keyword handling for animatable properties
Added inital keyword test
Removed redundant checks in fontWeightType
Changed addKeywordsToType() to typeWithKeywords()
Changed formatting
Moved assert comment
Fixed falsy logic bug
Style changes
Merge pull request #370 from alancutter/supportNontransitionalKeywords

Support CSS keyword values (aliases and non-transitional)
Moving the raf stuff into a class rather then functions with gloabl state.
Reworking the test-runner state transitions to make both running and posting only allow one at a time.