[Tinymux] Adding Penn's fmod function

[Stephen Dennis]

It shouldn't be hard to add FMOD(). I'll  try to get it into the next
drop of 2.4.0.23. That may not do you much good. But, at the least, it
would be a better starting point for a patch to 2.3.5.24 than the Penn
hardcode.

Only relying on softcode, the following is less tidy than using fmod,
but it does calculate the same answer:

     mul(2.5,sub(fdiv(6.1,2.5),floor(fdiv(6.1,2.5))))

Brazil