Add Either library, change Maybe API, and add tap to Touch library.
Switch how ADT's are displayed. Should have no visible effect.
Add the `mergeEither` signal and remove some dead code from Touch.js.
Ensure that touch listener is detached if it is not used.
Add type hints for new libraries, and fix the types of fps and fpsWhen.
Update runtime.
Add `xor` function.
Merge branch 'master' of https://github.com/evancz/Elm