Merge pull request #990 from JoeCreates/dev

Fix for rendering issue whereby some sprites positions were rounded instead of floored
FlxPoint: added add() and addPoint()
FlxVector: fix spelling of "subtract" in functions
FlxVector compile fix
No need to implement interface that the super class already implements
FlxG.resetGame(): fix some variables not being reset to default
Update CHANGELOG.md
FlxGamepad: use arrays instead of maps, closes #971

not a good idea to iterate over maps every frame
Fixed gamepad support in Flash.
Adding warning about unnecessary memory allocations in FlxGamepad (flash target only).
Memory optimization during FlxGame.update.
Adding warnings about memory allocations due to iterating Map datatypes every frame.
Comment style fix.
Improved how FlxSprites can be made flippable
Merge branch 'dev' of https://github.com/HaxeFlixel/flixel into dev