mark stop, skip, @epochs as deprecated

[mcabbott]

Replaces #1913 with the simpler plan to remove these from Flux 0.14.

Closes #1913

[Saransh-cpp]

Should the occurrences of stop, skip, and @epochs be removed from the docs, or should this wait till they are removed (v0.14)? The doctests are failing due to the deprecation warnings. Should the doctests be removed, or should they be updated with the warnings?

[mcabbott]

That's a good question. I think that:

• For the dep-warns to be of any use, I guess this must be merged into a 0.13 release.
• The removal of both the code and the docs should be in 0.14, thus a different PR
• Possibly the last 0.13 docs should have a warning note added too? That could be this PR.
• To keep tests passing, maybe this PR should also remove some jldoctest annotations.

[mcabbott]

@Saransh-cpp maybe you know, are the built docs previewed somewhere? Is this !!! note thing going to work?

[Saransh-cpp]

@mcabbott the previews are only generated if a PR is created from a branch belonging to the root Flux repository (restrictions from Documenter.jl). If the PR is from a branch belonging to the root repository, adding the documentation tag to the PR will trigger the DocBot to comment the generated URL.

[Saransh-cpp]

!!! note works! Tested locally!

[mcabbott]

Ready to merge?

[ToucheSir]

A bit of wordsmithing, but otherwise good to go