Now runs on a client-server model.

The queuing program is now split into two parts:

 - mdrunr.py sets up a queuing server that can holds the queue,
   launching jobs when it can.
 - mdclient.py is a client program that lets the user connect to the
   server and add jobs.
Added basic usage information.
Added "list_jobs" function to mdrunr, and refactoring.

Mdrunr class now keeps a dictionary of { job : status }, as well as the
queue, to maintain a history of what happens to each job. This history
can be polled using the q.list_jobs() method, where q is a Mdrunr
instance.

I also did some refactoring of Mdrunr, and extended the docstring.j
More usage information.