Mail-deduplicate

- Add supports for `Babyl`, `MH` and `MMDF` mailbox types.
- Add new `-f`/`--sources-format` option to force the type of mail
sources on opening.
- Add new `-u`/`--force-unlock` option to force the removal of a lock on
mailboxes on opening.
- Split-up the selection of mails candidate for removal and the deletion
itself into two distinct batch operations.
- Add issue templates to guide users to report bugs and request
features.
- Upgrade to `Poetry 1.1.0`.
- Test publishing to PyPi in dry-run mode by the way of Poetry.
- Auto-optimize images.
- Auto-lock closed issues and PRs after a moment of inactivity.

- Removes the `hash` subcommand. Replaced it with a `--hash-only`
parameter to the main dedupe command.
- Removes `deduplicate` subcommand. `mdedup` is now a simple CLI.
- Fix calls to deduplication strategy. Closes {issue}`86` and {issue}`88`.
- Fix computation of stats. Closes {issue}`89`.
- Drop support for Python 2. Refs {issue}`90`.
- Bump minimal Python requirement to 3.7.
- Repackage project around Poetry and `pyproject.toml`. Get rid of
`setup.py`.
- Replace unmaintained `bumpversion` by `bump2version`.
- Drop dependency on `progressbar2` and replace it with `click`'s.
Closes {issue}`37`.
- Switch from Travis to GitHub Actions for all CI/CD jobs.
- Regularly run unittests against Windows, Linux and macOS.
- Removes all copyright dates.
- Auto-fix Python format, typos and JSON content.
- Let dependabot check for dependencies and update them.
- Keep `.gitignore` and `.mailmap` up to date and in sync.
- Auto-publish package on tagging events via `twine`.
- Always run test build and check resulting package on each commits.
- Use declarative JSON to maintain list of GitHub labels for issues and
PRs.
- Lint both Python code and YAML content on each commit.
- Run unittests in random to order to detect coupling.

- Add explicit warning in CLI output to warn about 3.x branch
deprecation. Refs {issue}`180`.

> \[!CAUTION\]
> As of `v3.0.0`, the project has been renamed to *Mail Deduplicate* and is
> now available on:
>
> - Github at https://github.com/kdeldycke/mail-deduplicate
> - PyPi at https://pypi.org/project/mail-deduplicate

- Rename project from `maildir-deduplicate` to `mail-deduplicate`.
- Rename `master` branch to `main`.
- Add support for mboxes. Closes {issue}`48`.
- Remove requirement on `-s`/`--strategy` parameter, to let mails being
grouped into duplicate sets without any removal action, effectively
acting as a second-level dry-run.

> \[!WARNING\]
> This is the last version of the project known under the name *Maildir Deduplicate*
> (a.k.a. `maildir-deduplicate`).

- Add disclaimer to prepare project name change.
- Fix Header being object instead of string (61).
- Make body_lines conversion more reliable.
- Fix bugs in counter statistics ({issue}`45`, {issue}`57`).
- Add Message-ID as a header to check.
- Fix `UnicodeDecodeError`. Closes {issue}`53` and {issue}`55`.
- Bump requirement to `click_log >= 0.2.0`. Closes {issue}`58`, {issue}`59` and {issue}`60`.
- Replace `nose` by `pytest`.
- Only notify by mail of test failures.
- Drop support of Python 3.3.

- Fix rendering of changelog link in RST.
- Show selected log level in debug mode.
- Test builds against Python 3.6 and 3.7-dev, and most recent PyPy
targeting Python 2.7 and 3.3.
- Bump requirement to `readme_renderer >= 16.0`.
- Skip sets with unparsable mails because of incorrect encoding. Closes
{issue}`47`, {issue}`41` and {issue}`39`.
- Require the `-s`/`--strategy` CLI parameter to be set. Closes {issue}`44`.