PBR setup.cfg metadata conflicts with setuptools metadata

[cmcginty]

At some point PBR and setuptools started supporting the same fields in setup.cfg, but the keys are not the same. Since PBR is an extension of setuptools, it makes sense that PBR should not break the builtin fields supported by setuptools.

Some example is:

      setuptools vs PBR
"description" | "summary"
"long_description" | "description-file" or "description"

It also would be nice if you document the combined setuptools and PBR fields to make it easier to implement a fully working PBR-styled setup.cfg. I imagine most users do not understand there are additional fields that can be added in setup.cfg since they are not documented on the PBR user guide.

For example "long_description_content_type" works in both setuptools and PBR, but is never documented in PBR.

[Jan Vlčinský (jan-vlcinsky)]

Note, that "description-file" differs from "long_description" in that "description-file" is name of a file to read the description from in contrast to content itself in "long_description".