docs/esp8266: Add ESP8266 tutorial.

docs/esp8266/tutorial/neopixel.rst

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+Controlling NeoPixels
+=====================
+
+NeoPixels, also known as WS2812 LEDs, are full-colour LEDs that are connected in
+serial, are individually addressable, and can have their red, green and blue
+components set between 0 and 255.  They require precise timing to control them
+and there is a special neopixel module to do just this.
+
+To create a NeoPixel object do the following::
+
+    >>> import machine, neopixel
+    >>> np = neopixel.NeoPixel(machine.Pin(4), 8)
+
+This configures a NeoPixel strip on GPIO4 with 8 pixels.  You can adjust the
+"4" (pin number) and the "8" (number of pixel) to suit your set up.
+
+To set the colour of pixels use::
+
+    >>> np[0] = (255, 0, 0) # set to red, full brightness
+    >>> np[1] = (0, 128, 0) # set to green, half brightness
+    >>> np[2] = (0, 0, 64)  # set to blue, quarter brightness
+
+Then use the ``write()`` method to output the colours to the LEDs::
+
+    >>> np.write()
+
+The following demo function makes a fancy show on the LEDs::
+
+    import time
+
+    def demo(np):
+        n = np.n
+
+        # cycle
+        for i in range(4 * n):
+            for j in range(n):
+                np[j] = (0, 0, 0)
+            np[i % n] = (255, 255, 255)
+            np.write()
+            time.sleep_ms(25)
+
+        # bounce
+        for i in range(4 * n):
+            for j in range(n):
+                np[j] = (0, 0, 128)
+            if (i // n) % 2 == 0:
+                np[i % n] = (0, 0, 0)
+            else:
+                np[n - 1 - (i % n)] = (0, 0, 0)
+            np.write()
+            time.sleep_ms(60)
+
+        # fade in/out
+        for i in range(0, 4 * 256, 8):
+            for j in range(n):
+                if (i // 256) % 2 == 0:
+                    val = i & 0xff
+                else:
+                    val = 255 - (i & 0xff)
+                np[j] = (val, 0, 0)
+            np.write()
+
+        # clear
+        for i in range(n):
+            np[i] = (0, 0, 0)
+        np.write()
+
+Execute it using::
+
+    >>> demo(np)