MultiDocumenter vs Pollen

[sethaxen]

We have 2 main options for building unified docs with the docs for all sub-packages:

MultiDocumenter

When run, MultiDocumenter retrieves the most recent docs build for each subpackage and stitches them together with a menu bar and a unified search feature. Since it operates on pre-built docs, cross-references between packages operate using hard coded hyperlinks. The best current example of this is https://docs.sciml.ai/, whose source is in https://github.com/SciML/SciMLDocs/. This is probably the most ready option and the one I have started using in this package.

Pollen

Pollen is an (unregistered) docs package that allows for documenting multiple packages simultaneously. It doesn't use Documenter at all and instead takes its own docs approach, so it's missing some Documenter features but has other useful ones like function names in code examples being hyperlinks to the function docs (see lorenzoh/Pollen.jl#104 (comment)). It builds docs for all subpackages at the same time, so cross-referencing is possible. For example, there's this demo of SciML docs using Pollen: https://lorenzoh.github.io/SciMLDocs, whose source is https://github.com/lorenzoh/SciMLDocs/
Pollen should have an official release soon, when we could re-examine to see if it works for our use cases lorenzoh/Pollen.jl#105.

[sethaxen]

MultiDocumenter seems to work now. We might consider some reorganization of the docs. There's just one issue with search not working JuliaComputing/MultiDocumenter.jl#36

I've started work setting up a Pollen version of the docs at #2