Document CMath

Don't merge it now, I'll document more functions tomorrow. Just needed some review.
Remove maxv and try to be consistent with the style in the documentation of all methods. If you use `param vec Input vector` (the first word starting with capital after the argument name, then you should do the same for all methods, e.g. `param a Complex number` above. Since most of the methods don't do this, I suggest you to just start with small letters here as well.