This is relevant for SmartyStreets, and seems like a good idea in
general (possibly supported by other APIs).

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.

If you do this:

  Geocoder::Query.new("Kremlin, Moscow", :params => {:language => "ru"})

you should get a response in Russian ("ru") regardless of the value set
in Geocoder.configure(...).

Also add test for method presence in all lookups.

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.

Also move some lookup-related methods to Geocoder::Lookup module.