Allow passing message flags to a signal definition #145

I have a requirement to be able to set MessageFlag.NO_REPLY_EXPECTED on signals sent, because I have other processes on the same system that somewhat stupidly reply to my signals with an empty body, and because of the relatively high amount of traffic it increases CPU use on the embedded target that it runs on.

Presently this does not appear to be possible.

Maybe it is as simple as adding a flags parameter to the @signal decorator.