Setup Documenter

[gdalle]

Hi there,
I just added a Documenter workflow with GitHub Actions to replace the old functions list in the README. @logankilpatrick I think you said you would be happy to review?
On a side note, since the Travis CI workflow hasn't been used in a year, maybe we could switch all of it to GitHub Actions? I'm no expert though, I usually copy the CI files from PkgTemplates.jl and it does the job ^^
Thanks in advance!

[gdalle]

Since I wanted to test deployment on my fork, one would have to change the GitHub username and stuff like that to make it work on JuliaMath/Combinatorics.jl

[logankilpatrick]

Yes happy to merge this, what other steps do I need to do after the merge to get this up? Just setup secrets for the repo?

[gdalle]

I never had to set up secrets for GitHub Actions, at least not with the CI files I put there (which are taken straight from PkgTemplates). However you will need to activate GitHub Pages in repo settings and point it to the correct branch and folder

[logankilpatrick]

Working like a charm: https://juliamath.github.io/Combinatorics.jl/dev/ thank you!!!