Determine if a TCP port is open

Summary:
Create SocketAddress as a representation of a protocol, IP, port set.

Make IP, IPv4 and IPv6 a hierarchy of object representing IP addresses.

Use the Socket extension, but fallback to fsockopen if it's not available.

Use case: cache library keruald/cache tests suite needs to test if
a memcached or Redis instance is available on localhost to run those tests.

Test Plan: Tested on keruald/cache draft implementation

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3230