support /usr/local/share/* installation

Currently, setuptools supports package installation to /usr/local/bin via entry_points in setup(). For all other files it appears that MANIFEST is recommended, which bundles non-code files into the package distribution directly. This is not useful for resources whose destination pathing is expected by system utilties - such as manual pages under /usr/local/share. This presents a large painpoint. Example: https://github.com/beetbox/beets/issues/1501#issuecomment-110141520

I see value in keeping package files as as discreet as possible, however the current API of entry_points leads to incomplete command line interfaces.

I think it would make sense to introduce support at least two additional parameters:

setup(
    ...
    manuals=['path/to/man.1', 'path/to/man.2'],
    share=['path/to/share/dir']
)

These resources would still be distributed via MANIFEST or package_data, but would now be accompanied by symlinks to the appropriate directories. This is similar to how Homebrew distributes resources out of the Cellar.

Start by tracing how setup() handles entry_points and how MANIFEST or package_data distribute non-code files. Define the behavior for manuals and share resources, including the expected symlinks under /usr/local/share, and verify that installation produces the intended paths without breaking existing packaging.