Add network field support to ASN database queries

[gregorybrzeski]

Extended the information returned for ASN queries by adding network information to the already returned AutonomousSystemNumber and AutonomousSystemOrganization. Network information is calculated based on the database tree information.

MaxMind GeoLite documentation lists the network as core information in the GeoLite2 ASN database.
source: https://dev.maxmind.com/geoip/docs/databases/asn/

Change supports queries for IPv4 and IPv6 addresses.

Changes implemented:

• calculate network in CIDR notation based on IP address and mask calculated from database tree
• created new function getOffsetWithPrefix() that in turn is used by rewritten getOffset() to be compatible with current code
• used getOffsetWithPrefix() in ASNReader
• added appropriate tests
• used only current dependencies

Inspired by MaxMind nodejs module: GeoIP2-Node

Let me know what you think.