Impl Send and Sync for Controller.

[adeschamps]

See #6

I believe these are safe to implement because of the reasons I describe in the comments of the impl blocks.

[JMurph2015]

I think we'd have to take a harder look at the C library before implementing Sync. I think Send is probably fine, but it's not actually even totally clear that Send is fair because the run-time initialization of the LED strip arrays in the ws2811_t structs could end up putting references to the same region of memory in those structs.

[JMurph2015]

Update: Reading a little more about the Sync trait in particular, I think that is viable, but I still don't know about Send for the Controller struct itself.

[adeschamps]

I'm taking another look at it, and in its current state Sync is not safe to implement because Controller also implements Clone - that would lead to pointer aliasing. Would it be possible to remove the Clone impl?

[JMurph2015]

Yeah I can't come up with a good reason it should implement Clone, however, I also don't have a great reason to believe it should implement Sync.