pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/music/play-tone.md

@@ -2,17 +2,17 @@
 
 Play a musical tone through pin ``P0`` of the @boardname@ for as long as you say.
 
-### ~ hint
+## ~ hint
 
 This function only works on the @boardname@ and in some browsers.
 
-### ~
+## ~
 
 ```sig
 music.playTone(440, 120)
 ```
 
-### Parameters
+## Parameters
 
 * ``frequency`` is the [number](/types/number) of Hertz (how high or low the tone is).
 * ``ms`` is the [number](/types/number) of milliseconds that the tone lasts
@@ -28,7 +28,7 @@ music.playTone(freq, 1000)
 ```
 
 
-### Using other pins
+## Using other pins
 
 Use [analogSetPitchPin](/reference/pins/analog-set-pitch-pin) to change that pin used to generate music.
 
@@ -36,7 +36,7 @@ Use [analogSetPitchPin](/reference/pins/analog-set-pitch-pin) to change that pin
 pins.analogSetPitchPin(AnalogPin.P1);
 ```
 
-### See also
+## See also
 
 [rest](/reference/music/rest), [ring tone](/reference/music/ring-tone) , [tempo](/reference/music/tempo), [set tempo](/reference/music/set-tempo), 
 [change tempo by](/reference/music/change-tempo-by)