Adding geometric distribution for GLM.jl

[ayushpatnaikgit]

The following is the summary of the changes in the following source files:

1. In docs/src/index.md:

• Added Geometric to the list of distribution in family, under the “Fitting GLM models” section

2. In src/GLM.jl:

• Exported Geometric

3. In src/glmtools.jl:

• Defined LogLink as canonical link function for Geometric distribution
• Defined glmvar function for Geometric distribution
• Defined mustart function for Geometric distribution
• Defined devresid function for Geometric distribution
• Defined loglik_obs function for Geometric distribution
• Added an example glmvar in docstring
• Added an example mustart in docstring

4. In test/runtests.jl:

• Added a test case of Geometric distribution with LogLink
• Added a test case of Geometric distribution with InverseLink

[codecov-commenter]

Codecov Report

Merging #480 (633ed64) into master (42a0d04) will increase coverage by 0.16%. The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
+ Coverage   85.12%   85.28%   +0.16%     
==========================================
  Files           7        7              
  Lines         827      836       +9     
==========================================
+ Hits          704      713       +9     
  Misses        123      123              

Impacted Files	Coverage Δ
src/GLM.jl	50.00% <ø> (ø)
src/glmtools.jl	83.80% <94.11%> (+1.09%)	:arrow_up:

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[nalimilan]

It would be good to document where the numbers in the "Geometric LogLink" test set come from

I don't think we note this in the code usually, I think the implicit assumption is that values have been checked against R, either directly or indirectly (here, by checking against NegativeBinomial which was previously checked against R).

[ViralBShah]

Bumping this - what remains to merge?

[nalimilan]

Thanks!