Make package directory and simplify package setup

[jmabry]

Closes #91

Tested successfully with

conda create -n pyaf3
conda activate pyaf3
conda install pip
pip install scipy pandas sklearn matplotlib pydot dill pathos sqlalchemy
pip install -e .
python tests/hierarchical/test_grouped.py

[jmabry]

@antoinecarme Please take a look at the proposed changes to setup.py right here. The significant change is that we are now only identifying a single "package" and adding __init__.py files to the package modules (TS, CodeGen, and Bench).

[jmabry]

There is no longer any need to copy files into the sub package directories at setup time. I think this a more standard approach for python packaging

[antoinecarme]

Did you test this outside conda ?