**additions**
- added dateutils requirement
- added authentication to pull so that private sregistry images can be pulled
- client.speak() now also calls `_speak()` for subclass to implement with extra messages to user.
- client._get_setting() and client._get_and_update_setting() retrieve / update environment settings
- `SREGISTRY_THUMBNAIL` can be set for upload to Google Drive (or other clients that have thumbnails)
- addition of the credential cache, so each client can have a private credentials file/folder if user enables
**bug fixes**
- record after pull doesn't override image, if one existed
**creation**
- addition of Google Drive client, and new "share" command!
- clients for Singularity Hub, Singularity Registry, Google Storage, and local use
- addition of (mostly complete) documentation, Changelog, and Singularity file
- this is the initial creation of just the singularity registry client, to be separate from
singularity python.