Redesign of my old socket server code:

 * fdes_stream to use stream references instead of pointers.
 * signal_handler now in its own project, and no longer a template
   parameter for socket server.
 * socket_server no longer blocks any signals. Programmer must do this
   with signal_handler, and should normally block at least SIGHUP.
 * socket_server no longer installs the signal handler. Programmer must
   handle this outside this code.
 * Moved service_class out of the template parameters. Instantiation is
   now socket_server<server_body<service_class> >

 * Copyright 2014 Bruce Ide
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.