Unmarked dependency on numpy.

[SerpentChris]

Steps to reproduce:

1. Make and activate a fresh virtualenv.
2. Install pyfma via pip
3. Run the command python -c "import pyfma; pyfma.fma(1,2,3)"

The result is ModuleNotFoundError: No module named 'numpy'.

What I expect is to either be able to use pyfma without numpy, or for pyfma to automatically have pip download and install numpy when I install pyfma. I'm not an expert at setuptools but I think the first case requires making numpy an optional dependency, while the second case requires making numpy a required dependency.