Update light_ws2812.c

added 20MHz
Update light_ws2812.h

added 20MHz
Update light_ws2812.c

corrected some comments
Update light_ws2812.c
Update light_ws2812.c

updated comments and changed order, so that the head description is at top which fit's to the 16MHz. changed a bit the comments from the 20MHz
Merge pull request #1 from denimjeans/master

20mhz atmega168