Issue #82: Implement mechanism for asking the user or a keyring for passwords (see: bugwarrior.config:get_service_password()).
Issue #82 related: Cleanup some debug statements.
Issue #82 related: Some pep8 cleanup.
Issue #82 related: Add example description for password lookup strategies.
Merge pull request #83 from jenisys/feature/ask_password

Implement issue #82: Ask for missing password or use keyring