* Turned <provider>_libs into an iterable
Modifications :
- added class LibraryList + unit tests
- added convenience functions `find_libraries` and `dedupe`
- modifed non Intel blas/lapack providers
- modified packages using blas_shared_libs and similar functions
* atlas : added pthread variant
* intel packages : added lapack_libs and blas_libs
* find_library_path : removed unused function
* PR review : fixed last issues
* LibraryList : added test on __add__ return type
* LibraryList : added __radd__ fixed unit tests
fix : failing unit tests due to missing `self`
* cp2k and dependecies : fixed blas-lapack related statements in package.py
Package repositories now look like this:
top-level-dir/
repo.yaml
packages/
libelf/
package.py
mpich/
package.py
...
This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).
