* riece-server.el: Implement flood protection.

* riece-server.el: Implement flood protection.
(riece-flush-send-queue): New function.
(riece-process-send-string): Use it.
(riece-seconds-to-time): New function.
(riece-time-since): New function.
(riece-time-less-p): New function.
(riece-reset-process-buffer): Reset riece-send-queue,
riece-last-send-time, riece-send-size.
* riece-options.el (riece-max-send-size): New user option.
(riece-send-delay): New user option.
* riece-globals.el (riece-send-queue): New variable.
(riece-last-send-time): New variable.
(riece-send-size): New variable.