pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/basic/show-number.md

@@ -6,12 +6,12 @@ Show a number on the [LED screen](/device/screen). It will slide left if it has
 basic.showNumber(2)
 ```
 
-### Parameters
+## Parameters
 
 * `value` is a [Number](/types/number).
 * `interval` is an optional [Number](/types/number). It means the number of milliseconds before sliding the `value` left by one LED each time. Bigger intervals make the sliding slower.
 
-### Examples:
+## Examples:
 
 To show the number 10:
 
@@ -26,7 +26,7 @@ let x = 1
 basic.showNumber(x)
 ```
 
-### Example: count to 5
+## Example: count to 5
 
 This example uses a [for](/blocks/loops/for) loop to show numbers ``0`` through ``5`` on the screen:
 
@@ -37,12 +37,12 @@ for (let i = 0; i < 6; i++) {
 }
 ```
 
-### Other show functions
+## Other show functions
 
 * Use [show string](/reference/basic/show-string) to show a [String](/types/string) with letters on the screen.
 * Use [show animation](/reference/basic/show-animation) to show a group of pictures on the screen, one after another.
 
-### See also
+## See also
 
 [show string](/reference/basic/show-string), [show animation](/reference/basic/show-animation), [Number](/types/number), [math](/blocks/math)