Added code to conver berkeley db to sqlite db

Since the berkeley db contains pickled keys (don't know why) it
cannot be parsed with normal sqlite. Therefore, functionality has
been added to this module to get every entry out of the berkeley db
and add it to a new sqlite db
Initial version of code to compute monthly data

Created a new module which will precompute the monthly data. That
is, it will compute the average rtt, prevalence, and persistence of
all paths.
Various bugfixes

Fixed a variety of bugs, primarily typos.
Merge pull request #4 from ben-jones/compute-monthly

Compute monthly data
Optimized monthly code

Optimized monthly code by reducing the number of passes needed to
compute prevalence, persistence, and avg rtt from 2 to 1
Merge pull request #5 from ben-jones/monthly-optimize

Optimized monthly code