Knowledge-clustering

- If an undefined knowledge can be added to more than two (already defined) knowledges, pick the knowledge with the smallest edit distance. (Suggested by Aliaume Lopez.)
- Now supporting documents in French, with the option `-l fr` or `--lang fr`.
- New command `addquotes`, which find where you might have missed some quotes in your document.

Fixed a bug introduced in v0.2.3: the empty word was not an accepted prefix

Implementing two suggestions of 5:

- The `cluster` command is now optional
- The notion and diagnose file are now required options instead of arguments

Automatic PyPI release