ability to register hostname with master

[70m6]

currently when you start a node with goroslib it registers itself and topics it creates under an IP address as seen here:

this is even the case when setting the Host variable within the NodeConf structure.

when using the basic rospy talker listener, we see here that it will use the hostname:

this unfortunately makes it so nodes running on another computer over the network cannot see the rostopics if ROS_IP or ROS_HOSTNAME are set properly on the remote.

i've looked through the code and it does seem like a larger change due to the fact that there is already ipv6 support built in,
i have a branch where i've made it work, but had to remove support for ipv6.