testing materials library build now
adding some docs and tests, reworking how `make_elements` works
removing some debug stuff / outdated questions in comments
Moving initialization of natural_abund_map out of toplevel, removing the set nucids in favor of natural_abund_map.keys, cleaning up imports and whitespace
mass file was not being copied over properly, now fixed
refactoring make_materials_library to expand everything. For some reason, not writing out to nuc_data.h5, however.
segfault hunting with material.cpp
Removing data_fill_value from material.cpp's write_hdf5 to avoid segfault
hopefully this fixes the python2 error in grab_materials_compendium
This should fix the UnicodeDecodeError
PEP8 stuff and Python3 str/bytes issue