esp8266: Add APA102 serial individually controllable LEDs support.

APA102 is a new "smart LED", similar to WS2812 aka "Neopixel".

docs/esp8266/quickref.rst

@@ -271,6 +271,26 @@ For low-level driving of a NeoPixel::
     import esp
     esp.neopixel_write(pin, grb_buf, is800khz)
 
+APA102 driver
+-------------
+
+Use the ``apa102`` module::
+
+    from machine import Pin
+    from apa102 import APA102
+
+    clock = Pin(14, Pin.OUT)     # set GPIO14 to output to drive the clock
+    data = Pin(13, Pin.OUT)      # set GPIO13 to output to drive the data
+    apa = APA102(clock, data, 8) # create APA102 driver on the clock and the data pin for 8 pixels
+    apa[0] = (255, 255, 255, 31) # set the first pixel to white with a maximum brightness of 31
+    apa.write()                  # write data to all pixels
+    r, g, b, brightness = apa[0] # get first pixel colour
+
+For low-level driving of an APA102::
+
+    import esp
+    esp.apa102_write(clock_pin, data_pin, rgbi_buf)
+
 WebREPL (web browser interactive prompt)
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