support multiple lookup keys

  * Lookup and insert geo infos (e.g. city) when the lookup keys are more than oen in record.
Merge pull request #6 from muddydixon/multiple_detect_geo

support multiple lookup keys
add test for multiple field of geolocate results
update README
release v0.0.6
Merge branch original 'master' into support-lonlat

Conflicts:
	README.md
	lib/fluent/plugin/out_geoip.rb
	test/plugin/test_out_geoip.rb