Replicat

- Now supports Python 3.8.

- Fix a regression in [1.2.1](https://github.com/vaultah/replicat/releases/tag/1.2.1) that caused CLI to ignore user-defined values for `-r`/`--repository`. See #15.

- Fix a minor oversight that caused the `-r`/`--repository` argument to disappear from the help message.

- Implement stricter and more efficient CLI argument parsing
- Speed up startup
- Avoid loading all the downloaded snapshots into RAM
- Add `--cache-directory` and `--no-cache` CLI options
- Add `replicat.__version__` and the corresponding CLI flag
- Send status messages to `stderr` instead of `stdout`

- Fix a B2 backend regression for access keys that aren't restricted to a single bucket
- Fix a minor bug in the appearance of progress bars displayed by `replicat delete`

- Add support for S3-compatible backends
- Improved B2 backend implementation