Complete repeating past analysis (Issue #31)

[mikemahoney218]

Adding code for #31 (I believe this closes the issue, but don't want to make that claim -- and if we decide we want to do more work on it, I think this PR should merge separately).

Summary: When looking at FBI data from 2014-2018, PA is typically the 13th-14th closest state to MA in terms of arrest rates, whether we look at raw arrest rates per capita or z-scale them.

Next steps: I think we need to decide if this satisfactorily addresses #31 or if we want more work in that vein.

• If we want to spend more time deciding if PA is worth pursuing as a proxy, I think we could easily spend more time doing clustering with this dataset -- we've only looked at euclidian distance so far, which is only one measure of distance; running kNN or similar might turn up something interesting
• If we decide we're done with #31, we then need to decide if we're confident pressing on with the PA data or want to examine other options
  • If we're confident pressing on with PA, #23, #8, #9 are natural next steps
  • If not, we should spend a little time looking into data availability for other states

[mikemahoney218]

Force merging this PR (with goals of still discussing/reviewing with @dawngraham next week, particularly in the context of issue #31 ).