Test for case-sensitive atomic symbols
Test for case-sensitive atomic symbols

Up until now, atomic symbols were case-insensitive (e.g., 'd' and 'D'
both stand for deuterium; but 'p' means proton and 'P' means
phosphorus).  The problem with case-insensitivity is that it allows
for sloppier and less consistent code.

StanczakDominik/PlasmaPy