Inline HSV to RGB conversion

This is a big update!  There is now an additional color mode that allows
for simple and efficient control of the WS2812 LED with
hue-saturation-value (HSV).  The new HSV mode fits the HSV to GRB
conversion into the spare time not used while bit-banging the data
stream.

The library and demos were updated to be easier to read and use.
Create README.md