Make python code a namespace package

Instead of using ``openelexdataia`` as the package name for the
supporting code for the data processing scripts, put everything
under a namespace package called ``openelexdata``.  Much like
our main data pipeline package, put each state's code in a subpackage
named ``openelexdata.us.STATE_ABBREV``.  For example, Iowa's package
would be named ``openelexdata.us.ia``.

In order to create the namespace package, and append the subpackages
to the namespace, we have to use the pkgutil package
(https://docs.python.org/2/library/pkgutil.html) and put this
in the ``__init__.py`` of the ``openelexdata`` and ``openelexdata/us``
directories:

```
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)
```