Canvaslms

- Adds more fields to users listings
- Changes to use sets to deduplicate results

Improves submissions commands, bugfix in user filtering.

Adds the `login` command.

- Refactors script.
- Match users by regex (not only Canvas ID)
- Allows filtering by Canvas groups and group categories.
- `submission` downloads text attachments, prints using pager.
- Improves help descriptions.

PyPI packaging of my old canvas script.