Add unit test directory

Tests should be written for use with nosetests.
Update pip.req for Python 3
Add ShrunkClient public API

ShrunkClient provides functions that interact with the underlying database. They
will be implemented in future commits.

The client should be flexible enough to allow the database to change without
affecting other parts of the code.
Fix constructor; add URL shortening

Fix constructor to use proper default Redis port and create a database object.

Add method to shorten long URLs. This sets information in the database except
for initializing the visit information; this will be part of a future commit.
Add get_url_info to ShrunkClient

Returns a Python dict containing information about the given shrunk URL.
Contents of the dictionary are subject to change based on database schema
version.
Add Redis queries

Add simple Redis queries, assuming a simple schema. This is probably going to
change in the near future, however.

Add function stubs for (possibly) required functions. These will be implemented
in a future commit.