Pull R list_urls from upstream.

Merge branch 'releases/v0.11.0'

Add first working version of enzo

Merge branch 'releases/v0.10.0'

Merge branch 'workaround/yt-py-pillow' into yt-dev-working-branch

Docs after efischer edited, but before merging with @adamjsteward's s…

…tuff.

Version bump to 0.9.1

- Bugfixes for spack find
- 0.9.1 can read specs from current develop.

Tag Spack version 0.9

- Tagging a version to include all that's happened since 0.8.17

- This is in anticipation of merging `features/cflags` and
  `features/newarch`, which will break the spec format.

- 1.0 will likely come after those.

SPACK-87: enable disabled git fetch tests.

Spack version 0.8.17

Minor release with documentation updates to Master.