sphinx: Mention sphinx "doctest always-pass" bug in affected travis-cmd.

* docs: readme: minors.
build & test: sync python.cfg with .travis.yaml.

* ci: Enhance tests, bypass setup_cmd:doctest always_ok bug 508 with
nosetest.
* build: Add usefull build-commands in `setup.cfg`.
* model: Move model-accessing code within validation-generators to avoid
premature errors when validating.
* model: Add doctests for validating model.