Fix `FlxCamera` jitters when following a target

Resolves the following issue:
 * https://github.com/FlixelCommunity/flixel/issues/5 - https://github.com/AdamAtomic/flixel/issues/227

Fix provided by [Krix](https://github.com/krix)
Rename `FlxSprite::simpleRender` to `isSimpleRender`

Will also avoid an error if the `target` object is not a `FlxSprite`.
Change `FlxSprite::isSimpleRender` into a function

Also does some minor cleanup of making sure brace placement matches the rest of the code, and removes one unecessary comment.
Merge pull request #134 from IQAndreas/fix-flxcamera-follow-jitters

Fix `FlxCamera` "jitters" when following a target