[Distutils] elements of setuptools/wheel/FHS file categories proposal

[Daniel Holth]

It might be helpful to discuss the fine grained install scheme
proposal as several proposals:

- Add more install paths (categories) to the set currently used by
distutils/sysconfig
https://docs.python.org/3/library/sysconfig.html#installation-paths .
Define sensible defaults for each platform.

- Allow the paths to be individually overridden for each installed
package, in the same way that python setup.py install
--install-purelib=/some-directory can override the categories we have
now.

- Record the { category : path } mapping used during installation.

- Provide an API mapping (distribution name, category, relative path
within category) to help applications using data that is only
accessible via the module loader.
https://docs.python.org/3/library/importlib.html#importlib.abc.ResourceLoader

- Provide an API mapping the same to paths on the filesystem.

- Make the recorded mapping available in a predictable location, so it
can be perhaps understood by non-Python code.

- Allow setup.py's setup() call to install files relative to each
defined category.

- Extend Python binary package formats to support the new categories,
so the { category : path } mapping can be set at install time and not
at build time.