Group development related files together

[alvyjudy]

Summary of changes

Built on top of #2425 , I modified the file position for development related docs and referenced them from the top index:

docs/
    index.rst (toc tree now points to development/index.rst)
    development/
        index.rst (originally development.rst)
        developer-guide.rst
        releases.rst
        history.rst

Note: I think this means the github PR prompt will also have to be modified as it points toward the developer-guide ( https://setuptools.readthedocs.io/en/latest/developer-guide.html) that is now in a different position

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d. See documentation for details

[webknjaz]

@alvyjudy

Note: I think this means the github PR prompt will also have to be modified as it points toward the developer-guide ( setuptools.readthedocs.io/en/latest/developer-guide.html) that is now in a different position

In this case, the change to .github/pull_request_template.md should be included in this PR so that it's atomic.
Another question that arises with relation to nesting: wouldn't it be better to switch to dirhtml Sphinx builder. It'd produce nicer URLs on RTD and would help with moves like this. cc @jaraco

P.S. This probably deserves a change fragment: https://github.com/pypa/setuptools/tree/master/changelog.d.

[alvyjudy]

@webknjaz regarding the changelog, @jaraco mentioned that it might not be necessary to put changelog to different phases of doc I'm not sure if we should add one here?

Thanks for the review :) See below for the changes.

[webknjaz]

@alvyjudy the changelog is indeed optional for non-essential changes but it's my personal opinion that it's nice to have it most of the time. It's totally up to you, though.

[webknjaz]

I've also noticed that format got renamed into deprecated/python_eggs but is still linked as "format" in TOC in development.rst. I'm trying to set up a strict mode for #2424 and discovered this among other missing references. Your move of development.rst in this PR is also going to break some of the links so please check the toctree in the new location, you'll probably need to take care of some other entries there too.

[webknjaz]

@alvyjudy hey, my PR has been accepted and yours now has conflicts. I'm not planning to submit any more substantial changes in the near future so it's safe for you to solve the conflicts/do rebase. Please also note that you'll probably need to update the PR description to match what's actually in the PR ✌️