Add pooling to FlxTweens - only works with ONE_SHOT tween types.
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into my-dev

Conflicts:
	flixel/tweens/FlxTween.hx
	flixel/tweens/misc/NumTween.hx
	flixel/tweens/motion/QuadPath.hx
FlxTween pooling: Several small fixes

- made get_pool() and pool private, moved them to the top as they are static fields
- made the tween constructors private
- fixed copy-paste error in some pool docs
Merge pull request #7 from Gama11/my-dev

My dev
Merge pull request #913 from gamedevsam/my-dev

Add pooling to FlxTweens - only works with ONE_SHOT tween types.
FlxTween: made singleVar() and multiVar() private, tween() should be used instead
Compile fixes
FlxSound: return FlxSound for chaining, compile fix for fadeIn() and fadeOut()
FlxTween: add sfx()
Fix FlxTween destruction / recycling