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()
Fix support for HTML5, smarter switching between render methods
Minor fix
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
FlxGradient bitfive compile fix
FlxPoint: add floor() and ceil()
Replace FlxObject.forceComplexRender by pixelPerfectRender (true by default), closes #912

This makes rendering more consistent across targets and allows more control over supixel rendering
Previously, there was no good way to achieve pixel perfect rendering on cpp targets without changing draw()
FlxText: add shadowOffset property (thanks @cwkx)