package python client for PyPI

This is one step toward resolving #2. The package can be installed with
pip like:
`pip install delphi-epidata`

Note: the file `delphi_epidata.py` is missing from the package dir. This
is simply to avoid (1) duplicating code within the repo while (2) not
messing up the code structure since other projects expect to find
`delphi_epidata.py` in a particular location.

To build a new release of the package, first copy `delphi_epidata.py`
into the package, then follow the instructions at
https://packaging.python.org/tutorials/packaging-projects/