Patch

Changes:
-Added missed Transform overloads to Vector2 and Vector3.
-Added arithmetical operators to Point. This must increase usability of this struct.(I think XNA developers just forget add this to XNA).
-Removed useless GetState overload method at Keyboard(I know, I know this is for backward compablility - but its so easy to change for the end-user, because its primary used in just one place at Update; I also examine XNA through reflector and found the code of PlayerIndex is not used in GetState method.)
-Added MouseState.Position property. - makes retrieving cursor position more easy.

PS. Phew, I finally examined how git system works.