Document plan for testing server module.

proto/src/server/testing/server.rs

@@ -1,4 +1,7 @@
 //! Provides utilities for testing protocol code.
+// TODO: Move this to a separate crate, so that it can be depended upon as a
+// dev dependency in tests and run standalone as examples. Layering should be:
+// solstice-client -(dev)-> solstice-server -> solstice-proto
 
 use std::io;
 use std::net::{IpAddr, Ipv4Addr, SocketAddr};