[WIP] Add detailed model descriptions to documentation

[ajinkya-k]

I wanted to document the exact formulas for the link functions, especially the less common ones such as CloglogLink and CauchitLink used and ended up writing some detailed docs. Comments would be welcome

See preview here: https://ajinkya-k.github.io/GLM.jl/models (note I used documentervitepress for preview only, that is not pushed in this PR)

TODOs

• write the "three components" GLM intro a la wikipedia
• add a table to summarize all distributions and the corresponding link and mean functions with formulas (like the table here)
• add cauchit and cloglog link
• add Gamma
• add text for all distributions documented on the home page

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.54%. Comparing base (78c3ee6) to head (3ef731d).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #593      +/-   ##
==========================================
+ Coverage   90.33%   90.54%   +0.20%     
==========================================
  Files           8        8              
  Lines        1107     1089      -18     
==========================================
- Hits         1000      986      -14     
+ Misses        107      103       -4     

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[ajinkya-k]

@dmbates @palday @andreasnoack Comments are welcome!

[ajinkya-k]

Can someone help me fill out this table? I want to include in the docs:

legend:
✅ = canonical link
✓ = can use with distribution
❌ = cannot use with distribution

Link\Dist	Normal	Bern.	Binom.	Gamma	Geom.	Inv-Gaussian	Neg-Binom	Pois.
Identity	lm	❌	❌	?	?	?	❌	❌
Cauchit	?	✓	✓	?	?	?	?	?
Cloglog	?	✓	✓	?	?	?	?	?
Inverse	?	?	?	✅	?	?	?	?
Logit	?	✅	✓	?	?	?	?	?
Log	?	?	?	?	?	?	✓	✅
NegBinomial	?	?	?	?	?	?	✅	✓