WIP rewrite the daemon

cmd subdir does not build on purpose, it's only left in tree to grab old
code and move it to github.com/zrepl/zrepl/daemon

daemon/serve/serve.go

@@ -0,0 +1,26 @@
+package serve
+
+import (
+	"github.com/pkg/errors"
+	"github.com/zrepl/zrepl/config"
+	"net"
+)
+
+type ListenerFactory interface {
+	Listen() (net.Listener, error)
+}
+
+func FromConfig(g config.Global, in config.ServeEnum) (ListenerFactory, error) {
+
+	switch v := in.Ret.(type) {
+	case *config.TCPServe:
+		return TCPListenerFactoryFromConfig(g, v)
+	case *config.TLSServe:
+		return TLSListenerFactoryFromConfig(g, v)
+	case *config.StdinserverServer:
+		return StdinserverListenerFactoryFromConfig(g, v)
+	default:
+		return nil, errors.Errorf("internal error: unknown serve type %T", v)
+	}
+
+}