Some CI steps prior to a new release

[jlperla]

@arnavs Maybe you help get this up and running with @ajozefiak

@arnavs if you want to guineapig this with github actions with the docs build, be my guest! Maybe it isn't so hard! The only setup thing to figure out is the documenter.jl stuff. I strongly prefer github actions even it isn't much work.

We want to do a few things to the SDO package prior to tagging a new release

• If we are sticking with .travis.yml then
  • Get rid of the anything to do with the atuomatica notebook and pdf build stuff in here for now https://github.com/QuantEcon/SimpleDifferentialOperators.jl/blob/master/.travis.yml
  • We now have better ways to automatically compile the PDF, but why don't we just leave it in the repo for now.
  • Change the notifications on errors to me.
• Lets lowerbound julia 1.3 in the package and any docs. Search for 1.1

Lets move the PDF into the repository here in https://github.com/QuantEcon/SimpleDifferentialOperators.jl/tree/master/docs/tex

• Get rid of the generate_tex.sh
• Look for places that reference the PDF and then just point it to this such as https://github.com/QuantEcon/SimpleDifferentialOperators.jl/edit/master/docs/src/index.md. Lets not worry about versioning... it can always point at master

Lets move the notebooks and generated HTML into the repository in https://github.com/QuantEcon/SimpleDifferentialOperators.jl/tree/master/docs/notebooks

• Add links in https://github.com/QuantEcon/SimpleDifferentialOperators.jl/blob/master/docs/src/notebooks.mddirectly here. And, yes, only at the master version.
• Any notebooks that just aren't working and are not going to work can be removed from the build process. For example, not sure LCP_advanced.jmd is needed to build or run.

For the notebooks, I think we should remove the package and manifest for now if these things are working. that is,

• Get rid of https://github.com/QuantEcon/SimpleDifferentialOperators.jl/tree/master/docs/notebooks TOML files
• Get rid of

  
  pkg"add InstantiateFromURL"

using InstantiateFromURL activate_github_path("QuantEcon/SimpleDifferentialOperators.jl", path = "docs/examples", activate = true)

etc. in the notebooks.  People can figure these packages out themselves for now.

[jlperla]

Note that the github action with documentation looks pretty simple... https://github.com/invenia/PkgTemplates.jl/blob/master/test/fixtures/DocumenterGitHubActions/.github/workflows/ci.yml

Getting the documenter secrets setup properly in https://help.github.com/en/actions/configuring-and-managing-workflows/creating-and-storing-encrypted-secrets#creating-encrypted-secrets would be nice. Much easier than spreading things around.