Update docstrings, remove ambiguities, add constructors.

Remove unused imports.
Add docstrings to functions.
Remove Matrix44.translation. Multiply a vector by
the matrix to get this.
Rename vector3|4.negative to inverse. This matches matrix.
Remove ambiguous conversions in object api Matrix44->Vector, etc.
Add Vector4.from_vector3 with w parameter, default w=0.0.
Add Vector4.xyw.
Version bump.