Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 handle_connection(Arg1, Arg2, Arg3)

 echo(Arg1, Arg2, Arg3)

 crash(Arg1, Arg2, Arg3)

 request_exit_server(Arg1)

 message_json(Arg1, Arg2)

 server_method(Arg1, Arg2, Arg3)

 find_handler(Arg1, Arg2, Arg3)

 dispatch_exception(Arg1, Arg2, Arg3, Arg4)

 server_error(Arg1, Arg2, Arg3)

 unknown_method(Arg1)

 unknown_method(Arg1, Arg2, Arg3)

 unknown_error(Arg1, Arg2, Arg3)

 parse_error(Arg1)

 invalid_request(Arg1)