Knowledge-clustering

**addquotes:** now recognising more delimiters, namely `\kl[your_knowledge]{blabla}`, `your_knowledge"` and `your_knowledge`.

- "Notion files" are now named "knowledge files", following the official `knowledge` terminology. As a consequence, the option `-n --notion` is now named `-k --knowledge`. (15)

**Bug fix**:
- *init:* now using "en_core_web_sm" and "fr_core_news_sm" pipelines instead of "en" and "fr" (9)
- *clustering:* plurals of acronyms are now always clustered together (11)
- *clustering:* hyphenations should no longer get in the was of the clustering algorithm (12)
- *addquotes:* `\kl{}` or `\intro{}` are no longer ignored (14)
- *addquotes:* commented lines are now ignored (13)

Bug correction: `spacy` was required to run `knowledge init` but was not an install requirement (thanks to Thomas Colcombet).

Fixing two bugs described in 7 and 8.

Bug fix: the standard library module `re` was in install_requires ; as a result, knowledge-clustering couldn't be upgraded to v0.3