Async: Separate out listener to listen on multiple addresses

[helje5]

Same like upstream: swift-server#91

The current setup is the original swift-server setup which only specified a single port. We really want to support multiple addresses, i.e. IPv6 and IPv4, multiple or single NICs, etc.

The change is pretty easy: Just add an array of addresses and a list of open 'listen' sockets. They can all dispatch back to the same accept queue.

The open part is how the addresses would be represented. Tcp/file/http/httpds URLs might be an option, but need to figure out whether it supports wildcard.