TMatrix.Inverse improvement

Hey,

While working on MaxB3D, I ran into an issue trying to implement my own project/unproject functions in Prime.Math3D (the matrix code is from MiniB3D). Having tried a few different options, I finally nailed it down to TMatrix.Inverse.

A bit of quick googling revealed how to calculate a proper inverse.

Obviously, the current functionality is sufficient for MiniB3D, so if you don't want to risk breaking anything (everything appears normal!), just close this request.

Just thought I'd try to contribute back to MiniB3D where I could as it has proved to be quite a useful learning resource.