Fix issue with FlxTimers never triggering callbacks. Added userData variable so users can store and access custom data in FlxTimer callbacks.
Inline optimizations for FlxPool.
Fixing issue with swap-n-pop technique and destroying pooled objects in TimerManager.
Fixed issue with reset function in FlxTimer.
Removed destroy function from FlxPool because it was confusing and could cause issues (dangerous to assume what is being pooled, just null out pool reference if you want to get rid of it).