pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/lessons/compass/activity.md

@@ -2,11 +2,11 @@
 
 Display the direction that the @boardname@ is facing using the compass 
 
-### ~avatar avatar
+## ~avatar avatar
 
 Welcome! This guided tutorial will show you how to program a script that displays the direction the @boardname@ is pointing. Let's get started!
 
-### ~
+## ~
 
 Create a loop that will continuously update the reading of the compass.
 
@@ -90,9 +90,9 @@ basic.forever(() => {
 });
 ```
 
-### ~avatar avatar
+## ~avatar avatar
 
 Excellent, you're ready to continue with the [challenges](/lessons/compass/challenges)!
 
-### ~
+## ~
 

docs/lessons/compass/challenges.md

@@ -24,7 +24,7 @@ basic.forever(() => {
 });
 ```
 
-### Challenge 1
+## Challenge 1
 
 Instead of displaying `N` when the @boardname@ is pointing North, display a star to indicate the north star.
 
@@ -54,7 +54,7 @@ basic.forever(() => {
 
 * Run your code to see if it works as expected
 
-### Challenge 2
+## Challenge 2
 
 Instead of displaying just `N`, `W`, `S`, or `E`, display the full word.
 
@@ -79,7 +79,7 @@ basic.forever(() => {
 
 * Run your code to see if it works as expected
 
-### Challenge 3
+## Challenge 3
 
 Display your own unique message for each direction.