Adds support for binding to an IP as well as a port

Appy currently listens on INADDR_ANY (0.0.0.0) and there is no way to change this behavior. This pull adds support for data/address and the ADDRESS environment variable to allow Appy to listen on any IP address bound to a local interface. In the case of a non-integer port number the address is not sent to the listen() call as the port may very well be a path to a UNIX socket.