Knowledge-clustering

- The `cluster` and `addquotes` commands now have an autofinder feature: if they are not specified, the `.kl`, and `.diagnose` files are automatically found in the current folder. (5)
- After clustering, indicate which files have been modified. (35)
- Automatically checks for newer versions when running any command (can be disabled with the `--no-update` option).
- `AP` is now a synonym for the command `anchor`. (24)

Minor changes:
- Fixed bug 43: hyphenation is now properly handled by `cluster`.
- Fixed bug 36: if the same `.kl` file in given multiple times, ignore the copies.
- Fixed bug 39: the imperfection of the stemmer was causing some problems when computing the distance between notions.
- Switched from using the `os` library to `pathlib`.

- The command `cluster` can now take **multiple knowledge files** as input.
- The command `addquotes` can now take **multiple knowledge files** as input.

**Bug corrections**:
- Fixed 33 (`clustering`): non-breakable spaces are now correctly taken into in the distance computation (bug reported by Antonio Casares)
- Fixed 32 (`addquotes`): there was a misalignment whenever tabulations were used.

**Misc**:
- All knowledge files now use the extension `.kl` instead of `.tex` (suggested by Aliaume Lopez)

Fixed some bug with click preventing knowledge to be used.

- Implemented 28: The `anchor` command was improved: now the introduced knowledge is displayed.
- Added a ``--version`` command.

**Bug corrections**:
- Fixed 25 (`clustering`): accents are now taken into in the distance computation (bug reported by Antonio Casares)
- Fixed 29 (`clustering`): plurals/suffixes are taken into account even for scope inference
- Fixed 30 (`addquotes`): scope should be handled correctly

**Misc**:
- The code is now *typed*!
- Introduced tests (run `make test` in the development environment).

Fixes 27.

Fixing 23.