Added an in-python popcount implementation used for experiment
Added an in-python popcount implementation used for experiment

Ends up being slower than the naive bin(x).count('1'), but left the
implementation there for reference if a C version is to be build in the
future.

Purg/SMQTK,Purg/SMQTK,kfieldho/SMQTK,Purg/SMQTK,Purg/SMQTK,kfieldho/SMQTK,Purg/SMQTK,Purg/SMQTK,kfieldho/SMQTK,Purg/SMQTK,kfieldho/SMQTK,Purg/SMQTK,Purg/SMQTK,kfieldho/SMQTK,kfieldho/SMQTK,kfieldho/SMQTK,kfieldho/SMQTK,kfieldho/SMQTK