pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/led/enable.md

@@ -6,11 +6,11 @@ Turns the LED screen on and off
 led.enable(false);
 ```
 
-### Parameters
+## Parameters
 
 * ``on`` is a [boolean](/types/boolean) that defines the on/off state of the screen
 
-### Example: Turning off the screen
+## Example: Turning off the screen
 
 This program turns off the screen when pressing button ``B``
 
@@ -20,7 +20,7 @@ input.onButtonPressed(Button.B, () => {
 });
 ```
 
-### Pins: P3, P4, P6, P7, P9, P10
+## Pins: P3, P4, P6, P7, P9, P10
 
 These pins are coupled to the LED matrix display, and also it’s associated ambient light sensing mode.
 To disable the display driver feature (which will automatically disable the light sensing feature) call the DAL function ``led.enable(false)``. 
@@ -28,6 +28,6 @@ To turn the display driver back on again later, call ``led.enable(true)``.
 
 More information at http://tech.microbit.org/hardware/edgeconnector_ds/ .
 
-### See also
+## See also
 
 [unplot](/reference/led/unplot), [point](/reference/led/point), [LED screen](/device/screen)