- Finished adding documentation to existing methods of Vector3. 
- Added rajawali.math.vector package and moved Vector2 and Vector3 to
it.
- Added ImmutableVector3 which inherits from Vector3.
- Refactored more methods and moved some static members to Matrix4.
- Updated CHANGELOG.md

Signed-off-by: Jared Woolston <jwoolston@tenkiv.com>