Reorganise repository to more closely match Julia layout .....

This PR reorganises this repository to harmonise it with the ``Julia`` repository. 

  1. Updates ``quantecon/`` to ``src/``. [Note: This goes against some python style guides, but is useful in this instance to more closely match the repository structures between ``python`` and ``julia``]

@spencerlyon2 Given our test data files are currently pretty small - do you see a reason not to distribute them as part of the quantecon python package? 

@jstac This currently implements option 2, packaging the test data for distribution. Therefore when nostests runs it will technically import from the system installation and not the local package. Due to this fact, it may be more robust if we wrote a ``Makefile`` for `` make test`` which would install the latest and then run nosetests. 

Feeback / Comments most welcome.