Add CIDR and wildcard matching (rebased version of #21)

[akrabat]

This is a rebased version of #21:

Only activated if trusted proxy value contains a "*" (wildcard) or "/" (CIDR).
Uses strpos() on object-creation, so very low performance hit.
Tests are included.

I need CIDR matching for using this library within a load-balanced AWS VPC. There is no way to accurately predict the IP addresses for the load balancer nodes, you only know the IP range via CIDR block.