Adding the option of using a \* in the haproxy_hosts file.

This allows us to use the PROXY commands in environments where the IP address
of a load balancer isn't known (such as EC2).
Updating the PR to use ipaddr to determine whether
a remote IP address matches an ip address in the haproxy_hosts list.
Updated the associated docs.
Merge pull request #484 from fredjean/master

Adding the option of using CIDR ranges in the haproxy_hosts file.