task/defect-de-04-01 -- Create generic string-based hashing function

nparcel/bin/nppod
* provide a simple CLI that can identify an archived POD on the
  filesystem (or produce resultant directory structure if the POD is
  not archived)

nparcel/utils/files.py
* new method gen_digest() where given a string, create a standard and
  unique identifying token
* new method gen_digest_path() that builds consistent directory
  structure based on identifying token that evenly distributes PODs
  across the filesystem