Add a glossary entries for HoTT, UH, TC, fbip, dot notation and API

[gabriel-doriath-dohler]

These terms and acronyms could be difficult for newcomers depending on their background:

• HoTT: Homotopy Type Theory
• UH: Unification Hints
• TC: Type Classes
• fbip: Functional But In Place
• dot notation: field notation: generalized structure projection
• API: Application Programming Interface

[Julian]

(#249 gave us HoTT, so we can cross that one off).

I'll hit API at some point soon.