Core: rework socket layer, closes #939 @6h Rework the ip_connector and ip_acceptor to be more easy to use. Also, ip_connector will now use a resolver to find appropriate endpoints. Bring back full support for IPv6/IPv4 with all possible combinations. The tls_stream class now owns a shared ssl::context that is copied from the acceptor or the connector. The tls_connector and tls_acceptor wraps basic ones for convenience and simplicity. Irccd and irccdctl now support local SSL sockets.

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