pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/bluetooth/advertise-url.md

@@ -4,7 +4,7 @@ Advertises a URL via the Eddystone protocol over Bluetooth.
 
 ## ~hint
 
-### Eddystone
+## Eddystone
 
 Bluetooth beacons are used to indicate proximity to a place or object of interest. 
 Beacons use Bluetooth advertising to broadcast a small amount of data, 
@@ -21,13 +21,13 @@ Read more at https://lancaster-university.github.io/microbit-docs/ble/eddystone/
 bluetooth.advertiseUrl("https://makecode.microbit.org/", 7, true);
 ```
 
-### Parameters
+## Parameters
 
 * ``url`` - a [string](/types/string) containing the URL to broadcast, at most 17 characters long, excluding the protocol (eg: ``https://``) which gets encoded as 1 byte.
 * ``power`` - a [number](/types/number) representing the power level between 0 (short) and 7 (maximum range).
 * ``connectable`` - a [boolean](/blocks/logic/boolean) indicating whether or not the @boardname@ should accept connections. 
 
-### Example: Broadcast a secret code
+## Example: Broadcast a secret code
 
 ```blocks
 bluetooth.advertiseUrl("https://pxt.io?secret=42", 7, true);