Updates for pypixelbuf

[caternuson]

For #8

Updated to work with NeoPixel change to Pypixelbuf.

$ python3
Python 3.6.9 (default, Nov  7 2019, 10:44:02) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import board
>>> import neopixel_spi as neopixel
>>> pixels = neopixel.NeoPixel_SPI(board.SPI(), 8, pixel_order=neopixel.GRBW)
>>> pixels.fill(0xADAF00)
>>> pixels.brightness
1.0
>>> pixels.brightness = 0.5
>>> pixels.brightness
0.5
>>> pixels.brightness = 0.2
>>> pixels.brightness
0.2
>>> pixels[2] = 0xff0000
>>> pixels[4] = 0x00ff00
>>> pixels[6] = 0x0000ff
>>> 

[tannewt]

Did you consider inheriting from PixelBuf directly instead of NeoPixel?

[caternuson]

Did not. Just simply didn't think of it as an option.

Seems like a good suggestion though. I was sort of trying to do that by trying to find a way to reach past NeoPixel and be able to call Pypixelbuf's init directly. So it would set up the buffers. Couldn't find a way, so fell back to the manual setup, which is largely just copy-pasta from the two class's __init__()'s

I'll give that idea a try and see how it works out.