If you're using `setuptools` in an unusual way (and you are), please make sure the normal use modes don't work. about gprmax

[craig-warren]

As gprMax uses Cython extensions, I am following the guidance in the Cython docs which recommends building the extensions in the same location as the source files using python3 setup.py build_ext --inplace

http://docs.cython.org/src/reference/compilation.html#compiling-with-distutils

No other (normal) build or install steps are required.

I'll have a think if/how gprMax could be installed like a normal Python package.

[fake-name]

It doesn't necessarily need to be installable, just make it so the python setup.py install command doesn't produce a broken install.

If that output a "you're doing it wrong, do x instead" message, it would be completely fine.

[craig-warren]

Modified setup.py to handle plain build or install command line options.

[fake-name]

Thanks!