Include `setup.py` to install package and find submodules

[motiwari]

If you include a simple setup.py like the one below, you'll able to install your code locally as a Python module and import all subdirectories properly.

This will obviate relative package imports like here

Example setup.py:

from setuptools import setup, find_packages

setup(name='fastforest', version='1.0', packages=find_packages())