Fix matrix4 invert()

Signed-off-by: Aleksi Sapon <QcTechs@gmail.com>
Set all new components to zero when resizing a MatrixN

Signed-off-by: Aleksi Sapon <QcTechs@gmail.com>
Improve matrix tests in light of recent changes

Signed-off-by: Aleksi Sapon <QcTechs@gmail.com>