Merge branch 'develop' into barry/ceed

.codecov.yml

.travis.yml

README.md

bin/spack

lib/spack/docs/contribution_guide.rst

lib/spack/docs/developer_guide.rst

lib/spack/docs/packaging_guide.rst

lib/spack/docs/tutorial_sc16_modules.rst

lib/spack/env/cc

lib/spack/env/xl_r/xlc++_r

lib/spack/env/xl_r/xlc_r

lib/spack/env/xl_r/xlf90_r

lib/spack/env/xl_r/xlf_r

lib/spack/llnl/util/filesystem.py

lib/spack/spack/__init__.py

lib/spack/spack/build_systems/autotools.py

lib/spack/spack/build_systems/cmake.py

lib/spack/spack/build_systems/makefile.py

lib/spack/spack/build_systems/python.py

lib/spack/spack/build_systems/r.py