Create __init__.py

Creating the core subpackage which will store the main data objects, such as `Question`, `Answer`, etc
Create setup.py

Based on the setup.py used in sopython/sopython-site.
Added py.test to the requirements
Added basic fixtures

Added basic fixtures which pytest functions can use to access json files containing an example question and answer.
Added nidaba.features.util subpackage to hold the lower level feature extraction functions
Added nidaba.features._util subpackage to hold the lower level feature extraction functions.
Test fixtures working