added getMagnitude, setMagnitude, normalize and isZero methods to Point
Merge pull request #150 from beeglebug/master

added getMagnitude, setMagnitude, normalize and isZero methods to Point
Merge pull request #155 from alvinsight/dev

Tilemaps examples updated
Merge pull request #158 from alvinsight/dev

Invaders game improved
Group.callAll now supports nested functions and a context, making it really powerful!
Updated invaders demo.
Tidied up the code base