Parallel processing with multiprocessing

[fgregg]

First, let's implement parallel processing for a multicore machine using the python core library multiprocessing.

This is is useful in and of itself, but will also set us up for distributed computing.

Will close #111.

[fgregg]

When I run this code on mysql_example, it spawns eight processes, each of which takes about 3.1 gigs of memory. We need to figure out why these processes are using that much memory, and how to avoid it.