Create separate page for glossary of terms

[AnesBenmerzoug]

It is currently implemented as a tooltip.

[mdbenito]

Note that a glossary is more general than a list of abbreviations. If we include one, we are going to have to include many terms, and it's unclear whether one wouldn't be better served just with wikipedia links. Also, the line of what belongs in pydvl's glossary might become a bit blurry in time.