Added Matrix clearing methods

- Added ClearTranslation(), ClearScale(), ClearRotation() and
ClearProjection()
- Added ExtractProjection() to Matrix4
- Fixed ExtractScale() giving incorrect results if a Matrix4 contained
projection data
- Added setters to Matrix4d's Column properties
Merge pull request #10 from Artfunkel/master

Matrix ExtractScale() bug fix and "Clear" methods