Add pixelbuf for accelerating NeoPixel operations

[rhooper]

This PR adds a PixelBuf class that accelerates byteorder and brightness operations and will have an associated PR for https://github.com/adafruit/Adafruit_CircuitPython_NeoPixel
Relates to issue #884

Further work is needed to:

• disable for builds it doesn't fit into or make sense for
• add support for dotstars
• optimize it further (feedback please!)

[tannewt]

Thanks for taking this on! It'll be good to get it sped up. I think this can be simplified by keeping the API smaller and only working on a pixel basis, no raw byte stuff.

[tannewt]

@rhooper Are you waiting on me for this? It'd be awesome to get it in 4.0.0. Thanks!

[rhooper]

No, i'm not waiting on you, i'm waiting on my time to free up.
I did start on the classes for RGBLED and a Pure python pixelbuf
https://github.com/rhooper/Adafruit_CircuitPython_RGBLED
from which we can make NeoPixel and Dotstar (and others) inherit.

[rhooper]

Ideally to wrap this up, we'd pick up and use:

• master...rhooper:pixelbuf_byterorder_classes
  alongside python subclasses to drive specific types of things (either using C helpers, or by pulling out code into Python).

As well as finishing up the RGBLED so we have a fallback for hardware that doesn't fit the pixelbuf class:

• https://github.com/rhooper/Adafruit_CircuitPython_RGBLED/blob/master/pypixelbuf.py
  which isn't quite finished.

The RGBLED class might be better renamed to Pixelbuf. It is needed to be backwards compatible when we do a hard swap of NeoPixel and Dotstar (and others) to use Pixelbuf.

[tannewt]

Please let me know when this needs another look. Thanks!

[rhooper]

This is ready for another look, along with the code in:

• https://github.com/rhooper/Adafruit_CircuitPython_RGBLED/blob/master/adafruit_dotstar.py
• https://github.com/rhooper/Adafruit_CircuitPython_RGBLED/blob/master/neopixel.py
• https://github.com/rhooper/Adafruit_CircuitPython_RGBLED/blob/master/pypixelbuf.py

[tannewt]

Just a few questions and then it should be good to go. I think we should follow up with making the subclassing of PixelBuf work. The previous errors may have to do with the dunder methods.

[tannewt]

Looks good! Thank you for all of your hard work on this! I'll update the translations for you and then merge.

[tannewt]

Thank you so much for this!