Save the Largo Release Checklist in Largo's developer docs

[benlk]

Changes

This pull request makes the following changes:

• Copies a slightly-modified version of the Markdown checklist in Largo 0.6.4 release checklist #1704 into a copyable code block in a reStructuredText file, with some surrounding documentation and instructions on how to use the checklist. This addresses checklist for releases #809.
• Adds that file to the index of developer documentation
• Updates the API docs portion of the developer docs to use globbing to get all the docs files, replacing the previous hardcoded list
• Because of the new length of the API docs, moves the API docs to the bottom of the pages where it appears
• Moves the contribution and feedback sections of several docs to the top, so that they're above the API docs.

Why

For #809, and to improve largo.readthedocs.io

Testing/Questions

Features that this PR affects:

• https://largo.readthedocs.io

Questions that need to be answered before merging:

• are there any blatant typos?
• Do the post-release checklist items make sense?

Steps to test this PR:

1. In a new terminal —  here referred to as "terminal A" — spin up your Python virtualenv that contains sphinx: workon largo
2. Inside that virtualenv in terminal A, run grunt watch.
3. In a new terminal — here referred to as "terminal B" — do the following:
   • cd docs
   • touch index.rst (to trigger Grunt Watch's build of the docs)
   • cd _build/html
   • python -m SimpleHTTPServer (starts a simple HTTP server to give you local access to the docs)
4. In a browser, visit the URL that the Python server gave you
5. Poke around

[benlk]

I'm going to do the code-related changes for #1713 on this branch as well, because these changes are closely related.

[joshdarby]

@benlk The release checklist in here looks good.

[benlk]

@joshdarby if the changes in that commit look good, go ahead and merge.