1. Added herds so that in the Pryce scenario bulls are randomly
allocated to herds, rather than all bulls being considered for use in
all herds.

2. Fixed a typo in the setup step that caused bulls to only be 0.15 SD
better than cows for NM$ rather than 1.5 SD.

3. Fixed several typos, including one that caused cow information to be
written to a bull history file.

4. Piecemeal changes to better conform to PEP 8.