To run a single file, use:

  ruby -I test <filename>

GeoLite2 is a free version of a product called GeoIP2. Both use the same
format.

The result of the lookup in maxmind_local is stored at test/test_helper.rb to avoid the inclusion of maxmind's database in repository.

Make Geocoder.configure accept a hash (now preferred) and add
Geocoder.config method (for reading config). Deprecate old syntax.

This requires changing the way stubs work, so that they only simulate
actual HTTP calls, not cache hits.