Make sure that inmidi_clk() is called in the right place in the MIDI back-end. Fixes #255.
Note that I didn't fiddle with the implementation of the midiclkin object itself, which seems to be all right. I just made sure that it gets triggered in the appropriate place.
There isn't any useful documentation whatsoever for this object, so it's up to anyone's guess what the timebase for the time deltas in the right outlet should be. I've chosen msecs for now, which is in line with the default unit used by metro, delay, etc.
There is noticeable jitter in the time diff values, but that's to be expected with the simplistic implementation of midiclkin which just reports the deltas as they are. So in order to actually do some professional-grade tempo tracking or syncing with this thing, the user still has to think about some appropriate averaging process -- I'm not an expert on this, but I've been told that one can use PLLs = phase locked loops for that kind of thing.
Ok, there you have it. At least the object now does something sensible. :)