Consider exposing component/plugin API

[HadrienG2]

In principle, it is possible to extend hwloc by writing plugins for it. However, the compile-time constant used to evaluate ABI compatibility is a header define, which means I can't check it from Rust, so I'm not sure if exposing this from the Rust side is a good idea. It will probably require at least a little build.rs hackery to get back the define value into Rust.

In any case, here's the docs:

• High-level: https://hwloc.readthedocs.io/en/v2.9/plugins.html
• Discovery components: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__disc__components.html
• Discovery backents: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__disc__backends.html
• Generic components: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__generic__components.html
• Core component functions: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__components__core__funcs.html
• Filtering objects: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__components__filtering.html
• PCI discovery helpers: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__components__pcidisc.html
• Finding PCI during other discovery: https://hwloc.readthedocs.io/en/v2.9/group__hwlocality__components__pcifind.html

[HadrienG2]

This API is going to take significant effort to bind, and I cannot think of a good use case for it at the moment. If you would have an interest in it, please speak up and describe your use case a bit here!