MAINT: Add release notes and bump version

[larsoner]

1. Added a release_notes.rst generated with github_changelog_generator -- it works decently enough for a low-effort solution
2. Added a note about CSS that hopefully will be clear enough for users of sphinx_rtd_theme
3. Bumps 1.0.0.dev0 to 1.0.0

Closes #215

@rgommers feel free to look and merge if you're happy. Then my plan would be:

1. Make a release on GitHub, tagged as v1.0.0
2. build and twine upload the binaries to PyPI (someone would have to give me access permissions -- I'm "Eric89GXL" on there)
3. hope that RTD automagically updates the docs, if not, see if I can figure out how to make it happen (haven't worked with RTD yet!), though I'd probably also need permissions for that

Also happy to have someone else push out the release if they'd prefer to do so!

[codecov-commenter]

Codecov Report

Merging #264 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #264   +/-   ##
=======================================
  Coverage   92.66%   92.66%           
=======================================
  Files           7        7           
  Lines        1255     1255           
=======================================
  Hits         1163     1163           
  Misses         92       92           

[larsoner]

Actually I just noticed that release notes were kept, at least sometimes, on GitHub. Should I remove that page and just add the CSS notes when I cut the GitHub release? For now I'll just push a link to the releases page telling people to go there for info on previous releases...

[rgommers]

hope that RTD automagically updates the docs,

it indeed should do that

Actually I just noticed that release notes were kept, at least sometimes, on GitHub. Should I remove that page and just add the CSS notes when I cut the GitHub release? For now I'll just push a link to the releases page telling people to go there for info on previous releases...

This sounds right. I like the added release notes in this PR, no need to get rid of them. Then simple copy-pasting this into the GitHub Releases UI will get them there as well.

[rgommers]

Tested, looks good to me locally with Sphinx 2.4.4 - merging. Thanks @larsoner