P3 RGB pixel panel

@Gordon
Gave it a try and came down to 25 hz instead of 14 hz. This is still too slow, at least for ESP32.
Therefore I will go back to a special function outside the original Espruino code.
I opened a github repository for special code about 2 years ago and will bring it back to life
And maybe, I will spend some time on my makeFirmWare service, you never know

My ideas to speed up shiftout are

• split into 2 parts, first init and second shiftout data
  
• + init could be done before the loop
  
• + number of parameters for shifting is reduced
  
• - init needs to be done before, and data has to be stored somewhere
  
• instead of an sub array send start and length
  
• use a memory address instead of iterate
  
• + faster compared to iterate
  
• - works for large arrays only (?)
  
• one loop instead of jsvIterateCallback