Fixed Point.rotate bug . Also added a little documentation for world wrap. 

This is with reference to this [Issue #1079](https://github.com/photonstorm/phaser/issues/1079). 
Point.rotate was doing the math all wrong. Instead of rotating the point by the angle with respect to the *difference vector*, **rotate()** actually takes the angle with respect to the positive x-axis. 

i have fixed the same in this pull request and now it should work fine. 

Also added a small documentation note to world.wrap to make clear how to use it with sprites that have P2 bodies. (i made another pull request for that, but I dunno how it got pulled into this one too and I am a git noob to know how to get rid of it from this pull request.)