Fix in Vec2, LightingSystem does now NOT work

Removed Vec2::AngleBetween360, fixed Vec2::Angle and (hopefully)
Vec2::AngleBetween.

The LightingSystem's shadows are now literally half-broken, as they
depended on bad return values from the Vec2 implementation.
Fixed a bug in Get(World/Layer)Position
Merge branch 'master' of https://github.com/pimms/Pim