Knowledge-clustering

- When NLTK data is missing, raises the NLTK LookupError alongside with a knowledge error. (Improving 51.)

**Full Changelog**: https://github.com/remimorvan/knowledge-clustering/compare/v0.7.2...v0.7.3

- `cluster`: Added an option to print all new knowledges. (50)
- `init`: Better error message if you forgot to run `knowledge init` (51)

Bug corrections: 49 and 52.

**Full Changelog**: https://github.com/remimorvan/knowledge-clustering/compare/v0.7.1...v0.7.2

Bug corrections:
- 49 ImportError get_best_invocation_for_this_pip (reported by Clara Marcille)
- 46 Knowledges and comments are not detected in the line if there are extra spaces (reported & fixed by Théo Matricon)

- 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.