Reformat repository into a python package to make it installable

[dafrose]

• moved files around
• some cosmetic changes for pep8 compliance
• fixed python 3 compatibility in eddy_nlgc_mp.py (is this file still in use?)

[gagdiez]

tabs was literally invented to have the possibility of having different levels of indentation. tabs should always be preferred over a fixed number of spaces.

By using tabs we allow customizations that are essential for people with visual impairment. Custom tab-widths might seem like an unnecessary thing to most, but some people rely on it - and we can not ignore that.

[dafrose]

@gagdiez
PEP8 clearly states:

Spaces are the preferred indentation method.
Tabs should be used solely to remain consistent with code that is already indented with tabs.
Python 3 disallows mixing the use of tabs and spaces for indentation.
https://www.python.org/dev/peps/pep-0008/#tabs-or-spaces

[dafrose]

But thx for accepting. Does this mean the PR is accepted and can be merged? I honestly was not aware that anyone other than @mpaquette did maintain this repo :-D