Geocoding improvements -- addresses #96 and #117

I tried to do what was discussed in #96: first put the address through the Google Maps API, then get a normalized address string we can send to the DCGIS API. If you try it with the address that started all of this (1919 14th St NW, in the tweet referenced at the top of #96), you'll see the bug is fixed.

Probably we'll need a lot of regression testing, and we'd want some test cases that have more complicated addresses.

Since I was already in the area, I also tried to address the bogus address input problem (issue #117). Please see what you think of that.