Add math vector methods to FlxPoint (or create FlxVector)

[Dovyski]

Currently FlxPoint has one or two methods that can be used in math vector calculations. It's pretty hard to implement vector dependent functionalities using Flixel, such as steering behaviors. Useful methods such as rotate(), normalize(), perp(), dot(), cross(), etc are missing.

It would be great to have them. If they "clutter" the API, the FlxVector class could be created.

[Gama11]

Feel free to borrow some code from HaxeFlixel's FlxVector. :)

[Dovyski]

Consider it done! :) There are even more methods than I could thing of. Thanks!

[IQAndreas]

I added FlxVector to the FlxMath spreadsheet to make things easier to organize:

• Google Spreadsheet: FlxMath