Add FlxTypedSpriteGroup
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into FlxTypedSpriteGroup

Conflicts:
	flixel/group/FlxSpriteGroup.hx
FlxTypedSpriteGroup: opimization via statically typed _sprites array
FlxTypedSpriteGroup: also use _sprites for reset()
Make MouseEventManager compatible with FlxObject, closes #823
Update CHANGELOG.md
Fix support for HTML5, smarter switching between render methods
Minor fix
FlxGamepad: add some null checks for flash
Better handle sprite's "exists" and "visible" property.
Merge pull request #907 from kevinresol/dev

Better handle sprite's "exists" and "visible" property.
Minor cleanup for BitmapFrontEnd and TileSheetExt
Merge branch 'html5-fixes' of https://github.com/jgranick/flixel into dev
Remove unneeded html5 conditionals and logic
Fix unit tests
Make openfl-bitfive the default backend, closes #733
Use FLX_RENDER_TILE conditionals for the stats window
Enable middle and right mouse input in html5
Fix for FlxGamepad.pressed() in html5 by @YellowAfterLife
Enable sounds on html5, closes #728