Remove all python dependency

[matthewcarbone]

Currently, 95% of the codebase is written in C++ and all of the "heavy lifting" is done by C++. The last step, however, is done in Python and requires a NumPy dependency. The code's entire Python dependency is found in the postprocess.py file in the root directory of the project.

It would be fantastic to convert this into C++ so that everything can be contained in a single compiled binary. This will include rewriting a bunch of simple NumPy functions in C++. There are also some subtleties, since for example, correct calculation of the ridge energy observables uses the np.ma.* modules (masked arrays) distinct from the standard np.*. These allow for masking (expected) nan values.

The other complication is that I want to keep external dependencies to nothing. The only libraries hdspin depends on externally are MPI. I really don't want the code to depend on any other external programs/libraries.

So, long story short:

• Rewrite the postprocessing.py file in C++, integrating it into the hdspin source proper
• Integrate the post processing operation into the main code so that it runs after the simulations are complete
• [bonus] Make post processing MPI-enabled

Note: this is started here already: inc/array.h