only give the text remaining after the route

Since we set up the route, we know what the text starts with, or we
shouldn't care. Plugins/callbacks should not need to know how they are
being routed to. If we kept the route text in the message, the callback
would have to know what to ignore.

We may add the route as a new property to the Freyr::Message object if
it becomes necessary.
add say plugin to get the bot to speak

Using the say plugin, you can make the bot speak for you. Optionally,
you can make the bot address someone else.