Optimization of serial communication

[zaki0929]

Hi, davivid.
I updated this package to communicate serially only when the value changes. This saves extra serial communication.
I'm glad if you watch it in your spare time.

[vr4content]

To my understanding, this change breaks what dmx fixtures expect and should be available as an option. The standard protocol sends constantly the same value even with no changes. This protocol has no ack or way to communicate to the sender if the message has been arrive properly. Its made with the idea that in case that the receiver disconnect and connect again is able to recover to the status that should have. Some fixtures will support it and some fixtures doesn't. In case that all your lights support it, definitely can improve the performance, specially on usb interfaces with a low bitrate. Also its very interesting how, with this merge request, in theory we should have more "bandwidth space" available and the interface should be able to control more channels than the originally specified on the specs (if the driver allows you).