Add support for configuration inside 'setup.cfg'

[althonos]

While I am at it, I added support for green configuration inside setup.cfg, since there seem to be an almost official agreement about using this file for Python dev tools configuration.

setup.cfg is the only file where the [green] section is expected.

[coveralls]

Coverage remained the same at 100.0% when pulling 70488cc on althonos:feat-setupcfg into 8a7a0bd on CleanCut:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 70488cc on althonos:feat-setupcfg into 8a7a0bd on CleanCut:master.

[CleanCut]

Great start!

To change:

• setup.cfg should come first in the list, because we traverse the config file list in order and each later file overrides earlier files, which unintuitively means that the later an item is in the list, the more important it is. setup.cfg should be lower priority, so it should come earlier in the list.

To add:

• The documentation for config files needs to be updated in green/config.py. setup.cfg should be the new item 3, with existing items 3-5 becoming 4-6.
• Tests! Where are the tests?! ;-)

[CleanCut]

Also...I wonder if we should change our config-file resolution behavior from merge-all to "first config wins..." Something to ponder.

[CleanCut]

I've been pondering it. I like the current merging-of-configs behavior, I think.

By the way, if you feel like you need some help with my review suggestions, let me know and (I think) I can make a PR to your PR adding some of the stuff. If that helps.

[althonos]

Merging is okay, this allows changing some things locally while having a global configuration that is used everywhere, both of which can be updated independantly.

I do not agree with setup.cfg being the least in priority however, since it is a local configuration file (at the root of a Python project): it should have precedence over the global settings, as the .green file does.

EDIT: Oh, I see what you mean, not absolute first but just come before .green.

[coveralls]

Coverage remained the same at 100.0% when pulling 2379baa on althonos:feat-setupcfg into 8a7a0bd on CleanCut:master.

[CleanCut]

Yes, I meant switch it with .green. Sorry, I could have explained that more clearly.

[CleanCut]

Looks great!

[CleanCut]

Included in just-released version 2.9.0.