Annotate pylintrc w defaults and rationale

Generated from 'pylint --generate-rcfile'.

Defaults are commented out.

Exceptions to defaults include a rationale.

Note generation of 'pylintrc_reduced'.

Minor changes to code to conform w/ new config.
Isn't that a YAGNI?  `git grep unused_` didn't show any hits, and taking it out didn't cause `tox -e lint` to fail.