Added "Parallel programming with the multiprocessing library" lesson
Updated multiprocessing lesson to reflect reviewer comments
Addressed additional reviewer comments.  Ran through ispell.
Add a section on pickling
Merge pull request #1 from khinsen/multiprocessing

Add a section on pickling
Fixed grammatical typo
Changed the order in which parallel code is described to begin with
defining the work to be done (which follows the order in the complete
example source code)
Merge pull request #417 from selimnairb/master

Added "Parallel programming with the multiprocessing library" lesson