IPv6 support

[zmox]

If You can add surpport IPv6, it will be awesome~

[RosaryMala]

It doesn't accept connections from outside at all, so I don't see how this is needed.

[lethosor]

This is clsocket, not DFHack.

According to #4 (comment), there are some address resolution issues with this, but there's also some rudimentary IPv6 support in clsocket already (although probably not enough to do anything useful).

[hayguen]

At the moment even an Initialize() with IPv6 will produce an error ..
I had a look at this .. but at the moment i have no need for IPv6.