Add extra vector and matrix operations.

  For consistency, and also to share some code, made an internal single
implementation of several other functions, for example, v{2,3,4}_add,
m{2,3,4}_sub, etc.

  Renamed *_scale functions to *_muls, that is, "mul" by "s"calar.

  Implemented the new m4{f,d}_{translate,rotate,scale} functions.

  The code is being validated by comparing results with similar tests
using glm, and a note about a good share of the code (and more to come)
being translated from C++ glm templates has been added to ovecmath.c.