pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/control/in-background.md

@@ -7,15 +7,15 @@ control.inBackground(() => {
 })
 ```
 
-### ~hint
+## ~hint
 
 For more information, read 
 [The @boardname@ - a reactive system](/device/reactive).
 It is pretty advanced!
 
-### ~
+## ~
 
-### Example
+## Example
 
 This program shows how running in the background can say what is
 stored in a variable like `num`, while another part (``on button pressed``)
@@ -47,7 +47,7 @@ input.onButtonPressed(Button.A, () => {
 })
 ```
 
-### See also
+## See also
 
 [while](/blocks/loops/while), [forever](/reference/basic/forever),
 [on button pressed](/reference/input/on-button-pressed)

docs/reference/control/reset.md

@@ -8,7 +8,7 @@ This function is like pressing the reset button on the back of the @boardname@.
 control.reset()
 ```
 
-### Example
+## Example
 
 This program will count as high as you like when you press button `A`.
 When you get tired of counting, press button `B` to reset the
@@ -26,12 +26,12 @@ input.onButtonPressed(Button.B, () => {
 });
 ```
 
-#### ~hint
+### ~hint
 
 This program works better on a real @boardname@ than in the simulator.
 
-#### ~
+### ~
 
-### See Also
+## See Also
 
 [clear screen](/reference/basic/clear-screen), [game over](/reference/game/game-over)

docs/reference/control/wait-micros.md

@@ -6,7 +6,7 @@ Blocks the current fiber for the given amount of micro-seconds.
 control.waitMicros(4)
 ```
 
-### Example
+## Example
 
 This program sends a 10 micro-second HIGH pulse through pin ``P0``. 
 
@@ -21,12 +21,12 @@ control.waitMicros(10)
 pins.digitalWritePin(DigitalPin.P0, 0)
 ```
 
-#### ~hint
+### ~hint
 
 This function is not supported in the simulator.
 
-#### ~
+### ~
 
-### See Also
+## See Also
 
 [pause](/reference/basic/pause)