xlights 2017.21

XLIGHTS/NUTCRACKER RELEASE NOTES:
———————————

2017.21 Jul 28, 2017
— enh (keith) Add the block of channels model
— enh (keith) Add option to display fades as ramps on the On effect and Twinkle effect …
mainly for use in AC mode
— bug (keith) Fix a bunch of bugs with AC mode
— bug (keith) Fix #882
— bug (keith) Fix problem with oversize buffers crashing xLights