feat(filter): Remove RGN records (#354)

These records seem to correspond to large, non-administrative, regions
such as 'Northern Europe' and 'Southern California'. They feel very
subjective and don't map well into administrative hierarchies, often
coming up in unexpected search results.

There are only about 2200 and after a brief skim it looks safe to remove
them all.

Fixes #70

lib/streams/featureCodeFilterStream.js

@@ -2,7 +2,8 @@ var filter = require('through2-filter');
 var _ = require( 'lodash' );
 
 var unwantedFcodes = [
-  'RGNE', // economic regions. consists of multiple cities and is unwanted for geocoding
+  'RGN',   // large regions like 'Northern Europe' or 'Southern California' that don't fit well in admin hierarchies
+  'RGNE',  // economic regions. consists of multiple cities and is unwanted for geocoding
   'ADM1H', // historical
   'ADM2H', // historical
   'ADM3H', // historical