pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/reference/bluetooth.md

@@ -2,12 +2,12 @@
 
 Support for additional Bluetooth services.
 
-### ~hint
+## ~hint
 ![](/static/bluetooth/Bluetooth_SIG.png)
 
 For another device like a smartphone to use any of the Bluetooth "services" which the @boardname@ has, it must first be [paired with the @boardname@](/reference/bluetooth/bluetooth-pairing). Once paired, the other device may connect to the @boardname@ and exchange data relating to many of the @boardname@'s features.
 
-### ~
+## ~
 
 
 ```cards
@@ -41,11 +41,11 @@ bluetooth.advertiseUrl("https://makecode.microbit.org/", 7, true);
 bluetooth.stopAdvertising();
 ```
 
-### Advanced
+## Advanced
  
 For more advanced information on the @boardname@ Bluetooth UART service including information on using a smartphone, see the [Lancaster University @boardname@ runtime technical documentation](http://lancaster-university.github.io/microbit-docs/ble/uart-service/)
 
-### See Also
+## See Also
 
 [startAccelerometerService](/reference/bluetooth/start-accelerometer-service), [startButtonService](/reference/bluetooth/start-button-service), [startIOPinService](/reference/bluetooth/start-io-pin-service), [startLEDService](/reference/bluetooth/start-led-service), [startMagnetometerService](/reference/bluetooth/start-magnetometer-service), [startTemperatureService](/reference/bluetooth/start-temperature-service), 
 [startUartService](/reference/bluetooth/start-uart-service),