Read(max int) errors on system real time messages

[lucianthorr]

MIDI System Real Time Messages are captured by if event.Status&0xF0 == 0xF0 in stream.Read and return an error because they are not SysEx messages.

There's no data payload for system real time messages so I think there could just be a literal check for messages with a status between 0xF8 and 0xFF.
I'm happy to make that as a PR but I don't want to be presumptuous. I'm pretty new to this repo and to MIDI system messages in general.