Reorganization of code

[MilesCranmer]

Can we put all python source files into a delfi folder at the root of the project? So it would be, e.g., /delfi/ndes/... , /delfi/delfi/..., etc.

Then, instead of running:

import ndes

one would run

from delfi import ndes

This is in line with other python projects.

Btw, you can now run pip install git+https://github.com/justinalsing/pydelfi.git to install this project and the requirements.

[MilesCranmer]

Closed with #4.