0.2.1

• Added --address to ssdpy-server.
• Binding to an interface now explicitly subscribes the interface to the multicast group.
• Removed constants.IPv4 and constants.IPv6 in favor of raw strings: ("ipv4", "ipv6").
• Added code coverage reports.
• Added tests for ssdpy-server.
• Increase testing breadth to include more python versions (2.7, >=3.4).