Split Python Packages options and collect under common dir

[jorgepiloto]

Solves for #14 and will allow to start working on #10. This PR sets the base for creating any kind of template and reusing common files. New design is based on the following ideas:

• All family templates are collected under the same directory (e.g. templates/python, templates/fortran).
• The common/ directory contains shared resources across different family templates (e.g. templates/python/common).
• A cookiecutter.json is provided inside the templates/family/common/ and holds basic private variables. This ensures new families of templates need to override these vars in their custom cookiecutter.json.

Before merging this:

• Have a test dir per family template and a test script per each one of its members.
• Test project integrity and baked projects in the CI.
• Update doc about new usage and addition of new templates. Check README.rst too.
• Fix .pre-commit-config.yaml so it does not interfere with template files.

[jorgepiloto]

About cookiecutter template inheritance: cookiecutter/cookiecutter#1485

[jorgepiloto]

I'm facing some problems when trying to perform a "tree copy" of the common directory. See this warning in the official shutil docs.

[jorgepiloto]

I'm facing some problems when trying to perform a "tree copy" of the common directory. See this warning in the official shutil docs.

Solved locally! It was not a problem related with shutil but avoiding cookiecutter from parsing a literal {{...}}.

[jorgepiloto]

Problem: Once the cookiecutter context is initialized, additional copied files by the pre_gen_project.py are not rendered. This is because when the context starts it cannot be modified and those files are not present yet.

Solution: Create a function called bake_template which creates a temporary template directory. This temporary template will combine the common/ and the desired template/ files before executing the cookiecutter context.

I'm planning to take advantage of the tempfile module for this. Fingers crossed... 🤞🏽

Edit: It worked! 🚀

[jorgepiloto]

For the CI, I think the following approach should work:

• Add a flag in tox.ini so particular templates can be tested (e.g. `tox -e py310-keep-output-python).
• Add a .github/workflows/template_family.yml for testing baked projects (only linux-based in matrix.os).

[jorgepiloto]

Smoke tests in Python 3.7 are failing because shutil.copytree(dir_exist_ok=True) was introduced in Python+3.8.