Added a new geoip filter

Usage filter://geoip://?use_attr=postfix_source&save_latlon=true
Added debug logging & ignore empty results
lonlat defaults to true & saves an array of latlon for Kibana's bettermap
initial documentation for filter_geoip
initial documentation for filter_geoip.md
Merge pull request #42 from subutux/master

Added a new geoip filter