pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/led/plot.md

@@ -12,7 +12,7 @@ Use [unplot](/reference/led/unplot) to turn **off** an LED.
 
 ## ~
 
-### Parameters
+## Parameters
 
 * ``x`` is a [number](/types/number) that means the
   horizontal spot on the LED screen (from left to right: 0, 1, 2, 3,
@@ -23,15 +23,15 @@ Use [unplot](/reference/led/unplot) to turn **off** an LED.
 If a parameter is [out of bounds](/reference/out-of-bounds) (a value
 other than 0 to 4), then this function will do nothing.
 
-### ~hint
+## ~hint
 
 The LED screen is a solid square of LEDs with five LEDs on each side.
 To learn more about how you number the LEDs with ``x`` and ``y``
 coordinates, see [LED screen](/device/screen).
 
-### ~
+## ~
 
-### Example: One LED
+## Example: One LED
 
 This program turns on the bottom right LED.
 
@@ -40,7 +40,7 @@ led.plot(4, 4)
 ```
 
 
-### Example: Square
+## Example: Square
 
 This program uses a [for loop](/blocks/loops/for)
 and the `plot` function
@@ -56,13 +56,13 @@ for (let i = 0; i < 5; i++) {
 }
 ```
 
-### ~hint
+## ~hint
 
 Use the [point](/reference/led/point) function to find out if an LED is
 on or off.
 
-### ~
+## ~
 
-### See also
+## See also
 
 [unplot](/reference/led/unplot), [point](/reference/led/point), [LED screen](/device/screen)