geoip: add GeoIP2 and ASN support

* add GeoIP2 support
* load the ASN databases if present (v1 only, not available in v2, yet)

### Notes
* The ASN database is not yet available in the new GeoIP2 database format. 

### Todo
* ~~The ASN is available in the legacy format, but is not yet being utilized~~ Done.
* ~~It's two DBs, one for IPv4 and another for IPv6, so determine addr type first~~ Done.
is getting the ASN really dependent on $self->{_geoip2_city}?