These changes should make the library a swap in replacement
for code that uses the standard MicroPython builtin neopixel
library.

That is by replacing:

    import neopixel
    npixels = neopixel.NeoPixel(NeoPin,led_count)

with:

    try:
        import ws2812
        npixels = ws2812.WS2812(SPI_BUS,led_count)
    except:
        import neopixel
        npixels = neopixel.NeoPixel(NeoPin,led_count)

existing code that uses neopixels should work on boards with
the builtin library or boards that don't have the neopixel library
but have ws2812 neopixels connected to the MOSI pin of the SPI bus.