Inconsistent math api for quaternion based rotations

[ccummingsNV]

All the standard matrix_from_X functions, including those that only generate a rotation, return an affine 4x4 transform matrix. However matrix_from_quat returns only a 3x3 rotation matrix.

The float4x4 does have a constructor to go from float3x3, but it's not clear whether this populates m[3][3] with a 1 or not, which would be worth documenting if the intent is simply to convert immediately after use.