Simple IPv6 Support

[timcoote]

The dependent libraries used by RobotRemoteServer will work with IPv6, but this requires specific documentation and a small code modification (see Issue #60).

[timcoote]

fwiw, at least on Linux, IPv6 is a superset of IPv4. So that, using the example directory a RobotRemoteServer listening on "::" will work with tests.robot with {$ADDRESS} set to ::1, 127.0.0.1, and .

Even specific IPv4 addresses can be used with RobotRemoteServer on IPv6. However, they do require the correct IPv6 subnet. Thus "192.168.1.1" becomes "::ffff:192.168.1.1". Even "::ffff:0.0.0.0" listens on all IPv4 addresses!

I'm happy to create a PR to support IPv6, but I'm not clear on the best approach:
1- document the approach to changing the TCPServer address_family before importing RobotRemoteServer: non-breaking change, but quite a barrier to IPv6 adoption
2- change the universal address from 0.0.0.0 to :: and use IPv6 - this is a breaking change and would invalidate existing use of RobotRemoteServer. IPv4 addresses would need to be prepended with ::ffff:, 0.0.0.0 could, alternatively, be replaced with ::
3- create a new, extra, class for IPv6 - untested approach
4- munge IPv4 addresses to IPv6 versions within RobotRemoteServer - smells wrong, as it's unnecessarily complicated.

[pekkaklarck]

PR #64 covers this.