Add teardown phase to doctests

[lgoettgens]

Resolves #2058, resolves #2566.

This PR introduces the doc meta key DocTestTeardown and the jldoctest kwarg teardown, both of which contain code code that gets executed after the doctest itself. (after every block, let's keep the discussion about how to handle multiple same-named blocks in #2567).
If the Documenter maintainers (@mortenpi @fredrikekre ) still like this, I'll continue with adding this new feature to the documentation and add some tests.

My current only idea for testing is to add some print statements as teardown code and then compare the output, similar to the existing doctest tests in

Documenter.jl/test/doctests/doctests.jl

Line 184 in 7c1aea5

run_makedocs(["working.md"]) do result, success, backtrace, output

. In case of other ideas here please let me know.

cc @maleadt @fingolfin

[fingolfin]

Awesome, thank you!

For testing, you could also modify some global variable and observe the side effect? E.g. have a global counter that is incremented in setup and decrement in teardown and verify it is zero at the end, or something like that.

[fredrikekre]

Looks good to me, but please add some tests.

I think for global teardown you can just register something to run after makedocs(...) manually.

[mortenpi]

This looks great to me as well.

For testing, you could also modify some global variable and observe the side effect?

A global variable seems like a good idea to test this.