Add additional game loop events

Fixes #478 .
Add audio_isPlaying.
Refactor "Delay" to use dt from frameData

Rather than explicitly requesting the current time, the "Delay" component should just accumulate the time passed in by the "EnterFrame" event.  This way it doesn't need to worry about tracking the pause state of the game; that's all handled by the main game loop.

This meant drastically simplifying the tests -- they no longer need to overwrite the Date object or anything like that.
Merge pull request #775 from starwed/simpler-delay

Refactor "Delay" to use dt from frameData
Refactored loader; created function 'removeAssets'; fixed bug in Crafty.audio.remove
Merge pull request #778 from mucaho/audio_isPlaying

Add audio_isPlaying.
Merge pull request #769 from mucaho/more_events

Add additional game loop events
Merge pull request #777 from heniotierra/loader_refactored

Refactored loader, and created new function 'removeAssets'
Update DOM.js
Merge pull request #779 from truman/develop

Update DOM.js documentation typo