Provide a way to have reverse-geo lookups return partial data

[jpmens]

based on a question in #478 we might want to have a mechanism by which partial data obtained during a reverse-geo lookup.

Say a user wishes to have locality and cc only, a Recorder configuration (something along the lines of OTR_REVGEOFORMAT=$locality, $cc maybe) would have it store (and likely cache) only those two fields.