- split up bar and circular methods from my9221 into own libraries

- add a getLED to match setLED

- for bar, allow spec (via some method) to a specific bar

- examples for my9221, keep existing ones for bar and circular

- warning message if mmap gpio fails and more that 1 instance

- make sure ctor throws exceptions on gpio setup errors, as well as
  ensure at least one instance specified.

- reg map of commandWord bits and provide accessor methods (set/get)
