Added ability to remove server after adding.

src/copas/copas.lua

@@ -444,6 +444,13 @@ function copas.addserver(server, handler, timeout)
         addTCPserver(server, handler, timeout)
     end
 end
+
+function copas.removeserver(server)
+  _servers[server] = nil
+  _reading:remove(server)
+  return server:close()
+end
+
 -------------------------------------------------------------------------------
 -- Adds an new courotine thread to Copas dispatcher
 -------------------------------------------------------------------------------