Ref: #214

After reviewing the source for the send method, it seems that the function is not designed to be used in any place except the tail end of the middleware stack, since it throws (an HttpError with status 404) when there is no match.

This seems rather opinionated (which is fine), but it was not very intuitive for me, and I think it needs to be documented.

It would be nice to provide a configuration option for send (and context.send) so that this behavior can be changed — e.g. to allow invoking next (instead of throwing) when no match is found, so that it can used in other positions in the middleware stack.