Print algebraic form of AbstractFunction by default

[odow]

Closes #2111

Open to ideas for what we should print, exactly.

Docstrings can all be updated using --fix when building the docs:

julia> ARGS
1-element Vector{String}:
 "--fix"

julia> include("docs/make.jl")
WARNING: redefinition of constant _PAGES. This may fail, cause incorrect answers, or produce other errors.
[ Info: SetupBuildDirectory: setting up build directory.
[ Info: Doctest: running doctests.
[ Info: Skipped ExpandTemplates step (doctest only).
[ Info: Skipped CrossReferences step (doctest only).
[ Info: Skipped CheckDocument step (doctest only).
[ Info: Skipped Populate step (doctest only).
[ Info: Skipped RenderDocument step (doctest only).
  3.325270 seconds (4.70 M allocations: 319.401 MiB, 3.95% gc time)
┌ Warning: Documenter could not auto-detect the building environment Skipping deployment.
└ @ Documenter ~/.julia/packages/Documenter/H5y27/src/deployconfig.jl:75

[blegat]

Let's do #2111 (comment) for LaTeX

[odow]

Done

[blegat]

Looks good, thanks! I have a small suggestion but it's more of a why not so up to you