* 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
* Removing the nobuild, nolink, and alldeps dependency types in favor of being explicit.
* This will help with maintenance going forward, as adding more dependency types won't affect existing declared dependencies in weird ways.
* default deptype is still `('build', 'link')`
