Coltrane

- Clean up code.

- Better support for multiple domains and custom sites.
- Add `coltrane.toml` settings file.

- Automatically enable `dj-angles` if the library is installed.
- Experimental support for multiple domains.

**Breaking changes**

- Drop support for Python 3.8.
- Remove loading deprecated `data.json` file.

- Handle string, date, epoch in `publish_date` and convert them to timezone-aware datetime.

- Prevent missing `compress` templatetag from raising an error when calling the `compress` management command.

- Set `COMPRESS_OFFLINE=True` when running the `compress` management command.