pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/pins/on-pulsed.md

@@ -8,12 +8,12 @@ pulses **High** or **Low** (as specified).
 pins.onPulsed(DigitalPin.P0, PulseValue.High, () => { });
 ```
 
-### Parameters
+## Parameters
 
 * ``name``: The @boardname@ hardware pin to configure (``P0`` through ``P20``)
 * ``pulse``: Which state will cause the associated block to execute (**High** or **Low**)
 
-### Example
+## Example
 
 The following example configures pin ``P2`` for digital input,
 and then displays the string `LOW` whenever ``P2`` pulses low.
@@ -24,7 +24,7 @@ pins.onPulsed(DigitalPin.P2, PulseValue.Low, () => {
 });
 ```
 
-### See also
+## See also
 
 [servo set pulse](/reference/pins/servo-set-pulse),
 [pulse duration](/reference/pins/pulse-duration),