cpplib: Add a test project for mat3's inverse matrix
cpplib: Fix Mat3::inverse() did not return correct inverse matrix

We actually had to apply transpose before returning.
cpplib: Add test codes to measure computation time for matrix inverse
cpplib: Micro-optimize mat3 inverse method by factorize cofactors
cpplib: Add element-wise constructor to Mat3
cpplib: Add tvec3(), a transpose vector getter to Mat3 with tests