Use a command-line flag (-k) for the key file instead of an environment variable.
Add -c flag that reads the key from the output of a command.
Use "q" instead of "s" for secret questions (in the YAML and on the
command-line).  Also, print questions to stderr.
Add test suite.
Update README.
Bump version number: passwords are compatible but settings files with secret
questions must be updated.
yaml.safe_load is sufficient to read password settings.
Remove trailing whitespace.
Remove unused import.