Allow packaged resources and alternate extensions

[bckohan]

Thanks for a great utility. It's kept my Django settings sane for a few years now.

I manage several large Django projects with many apps that are deployed in multiple settings, each time having a different INSTALLED_APP stack. A pattern I've found immensely useful in this scenario is for my constituent app packages to include default settings files as packaged resources. I give them alternate extensions (i.e. .conf instead of .py) so my system knows which ones to automagically include.

I've been using an extended version of django-split-settings to accomplish this, but I think others could find this useful as well so I'm happy to submit my extensions as a PR.

For example, the idea is to be able to include packaged resources where your directory structure looks like:

mypackage
├── __init__.py
└── settings
    ├── __init__.py
    └── base.conf

As so:

from split_settings import include, resource, optional
from mypackage import settings

include(
    resource(settings, 'base.conf'),
    resource('mypackage.settings', 'base.conf'),  # alternate
    optional(resource(settings, 'local.conf')),  # optional can wrap resources too
)

Another nicety about using an alternate to .py for your settings files is that its a visual cue to other devs (and your IDE) that these files may not behave like typical python files on account of how split-settings sets their scope.