Improve method of building wheels

[johnaparker]

• Use miniconda to download Eigen3 and GSL, and use environments for each version of Python
• For each OS, this script should be slightly modified
• On Windows, the gsl.dll file needs to be packaged into the wheel (on *nix it's done with auditwheel)

Note
If the following bug occurs:

auditwheel: error: cannot repair "/io/.build_wheels/wheelhouse/miepy-0.5.0-cp38-cp38-linux_x86_64.whl" to "manylinux2010_x86_64" ABI because of the presence of too-recent versioned symbols. You'll need to compile the wheel on an older toolchain

it may be due to lingering .o or .mod files in the nfmds folder. Running make clean will remove all build files.