Fixed up the FlxShapes

Fixed a lot of inconsistency in the FlxShapes. Now the following should be true:

* Width/Height of shapes reflects underlying geometric boundaries (ignores stroke)
* Offset should be automatically set so that object's x/y matches expected position
   * X/Y = upper-left
   * Turn on debug lines, boundaries should be in the middle of the stroke (for a rectangle), etc.
That would be one option, but I'm not sure that part would belong in flixel-addons, as it's sorta specific to your particular xml format (I think?).