[WIP] Solving functions for Matrix2/3/4

I have started porting the solving methods from box2d. The code for solve3 is a bit verbose because I inlined the cross product code to not allocate vectors for each matrix column.

Additionally the code of solve in Matrix3 and solve3 in Matrix4 is completely duplicated. Currently I have no good idea to reduce the duplication.

Matrix4#solve is still missing.
Tests are still missing.