Pawpyseed

- Unit tested the flip_spin utility in the Projector class 9.
- Fixed memory leaks of the projector grids used in the C backend, which became an issue when many Wavefunction objects were loaded.
- Fix some symmetry operation issues 11.
- Fix default argument issues and incorrect naming for NCLWavefunction write utilities 12 13.

Fix minor bug in MomentumMatrix, improve error catching and documentation.

The DelocalizedStatePerturbationCorrection class has been added to pawpyseed.analysis.corrections to shift states based on their valence/conduction character AND how delocalized they are. This release also includes a fix for a bug that would cause a segfault for some POTCAR files.

This relatively large update contains several important features:
* The user now has different options for performing projections in the `Projector` class, which can be selected by the `method` input variable to `Projector`. One new method, `aug_recip`, is slightly faster and theoretically more precise because of lack of aliasing (though in practice there isn't a big difference, and `aug_recip` has some small (about 0.02) normalization issues to tough systems like vacancies. This is likely on the part of the DFT output though, not the method itself.
* `site.cfg.default` has been added, which provides a bunch of default build instructions for the C extensions. Users can override these options with `~/.pawpyseed-site.cfg`, and instructions for how to do so to get more reliable installations is in the README.
* Debug tools have been added (primarily for developers) to assess how good a basis set the partial waves are for a given pseudowavefunction. This is very preliminary, and just prints a bunch of values for now.

The most important item here is the ctypes->Cython conversion, which should improve portability and readability of the code. There is also a utility for perform a perturbation theory-based correction now.