recursive include all files of "project_slug" module on sdist and wheel package

[luzfcb]

if I include python submodules, and other folders inside package, the current configuration not include them in sdist and wheel package.

this pull-request resolves this (at least resolved to me).

I saw django doing the same: https://github.com/django/django/blob/master/MANIFEST.in#L9

[pydanny]

@luzfcb, @eliasdorneles, are there any reasons why this shouldn't be added to Cookiecutter PyPackage?

[eliasdorneles]

Hi! It's probably okay, I only didn't merge it because I didn't test it.