Not needed now that pre-commit runs in the .pre stage.

With the Toolbox container, I'm now on Python 3.9.

First of all, Poca 1.1 was released which contained my PR so using my
fork is no longer needed. Then various package updates from running
`pipenv update`.

My PR was merged and it also has other fixes I need.

Deduce the uid and gid from the volume owner and run as those. Don't
need to mount /etc/passwd and /etc/group inside the container (didn't
work with --user anyway). No hard-coded uids/ users anymore.

Don't use the host user home directory.

Install the version from my git fork which has a fix for a non-writable
config directory if the config file already exists.

This reverts commit fe7fdfb4. The image
is now available.

There aren't Alpine 3.13 tags for the Python image yet.

- More pre-commit hooks.
- Fixes from said hooks.
- pipenv updates.
- pre-commit updates.

The usage is completely replaced. Now locally I run inside a pipenv and
remotely using Docker.

- Use Supersonic as the Cron daemon.
- Run locally using pipenv.
- Run remotely using Docker (and docker-compose).
- Automate tasks using pipenv custom script shortcuts.
- Updated pre-commit hooks, added yamllint hook.
- Added license.
- Updated README.