Add instructions for making crypt salted hashes using Python and passlib

Quotes removed around salts and hashes in existing examples because, AFAIK,
base64-encoded strings contain no characters which must be escaped in YAML (the
following are not in base64: '!', ':', '|', '>').

Closes #293
Merge pull request #295 from ariddell/feature/passlib-crypt

Add instructions for making crypt salted hashes using Python and passlib