- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
- core and most packages are (Apache-2.0 OR MIT)
- a very small number of remaining packages are LGPL-2.1-only
* PackageMeta: `run_before` is an alias of `precondition`, `run_after` an alias of `sanity_check`
* PackageMeta: removed `precondition` and `sanity_check`
* PackageMeta: decorators are now free-standing
* package: modified/added docstrings. Fixed the semantics of `on_package_attributes`.
* package: added unit test assertion as side effects of install
* build_systems: factored build-time test running into base class
* r: updated decorators in package.py
* docs: updated decorator names
* New package h5hut -- High-Performance I/O Library for Particle-based Simulations
* Set up MPI compilers
* Add version 1.8.12 to HDF5
* Correct Sphinx error