* Change 'accessible' to align with React Native.
* Add support for 'importantForAccessibility'.
* Stop event propagation for keyboard-activated Touchables (nested
Touchables now respond the same as when touch-activated).
* Fix whitespace layout of nested Text elements.
* Use 'div' for Text to improve TalkBack grouping.
* Rewrite accessibility docs.
Close#382Fix#408
Shim the 'hitSlop' prop using a positioned element to extend the size of
a View's touch target without changing layout. Unlike the native
implementation, the touch target may extend past the parent view bounds.
