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.

v0.8.16 Release Notes

=========================

5 new packages since 0.8.15:
---------------------------------
 - cram
 - metis
 - otf
 - ravel
 - scotch
 - Fix for SAMRAI fetch URL.

For packagers
---------------------
  - MPICH now sets up MPICH_CC, MPICH_CXX, etc. in dependent environment
    so that dependency builds use Spack compiler wrappers.
  - Simpler build error messages on fail (no more python stacktrace)
  - Disable CMake policy warnings in `std_cmake_args`.
  - Remove superfluous compiler wrapper links (g++ link interfered with icpc)
  - Several new packaging helper functions:
    - `install_tree`
    - `traverse_tree`
    - `force_symlink`