Added code to split up monthly data by router

Added code to export_data.py which will split up the sqlite3 version
of the monthly database into a bunch of smaller databases separated
by the router. This is necessary 1) to do multitheading analysis
(sqlite does not support concurrency) and 2) to improve performance
by reducing the db size. This is a first step to running these
computations in parallel
fixed typo

fixed typo where a nonexistant variable was used
Initial commit of multithreaded code

initial (untested) version of multithreading code
bug fix

updated one filename to have the correct extension
working version of multiprocessor code

first working version of code to take advantage of multithreading
in python. the multiprocessing library claims true concurrency, but
it remains to be seen if the code will actually use multiple cpus
made precompute.py executable

Made precompute. py executable to make it easier to manage the
multithreaded interface and kill the many python interpreters if
necessary.

Note: the preffered way to call this is ./precompute.py
Merge pull request #7 from ben-jones/split-up-computation

Split up computation