pxt-microbit Accessibility PR (#529)

* Accessibility changes

docs/projects/light-monster/code.md

@@ -1,11 +1,11 @@
 # Code
-### @description code to make the coffee cup monster alive
+## @description code to make the coffee cup monster alive
 
-### ~avatar avatar
+## ~avatar avatar
 
 Add code to open the mouth when light is detected.
 
-### ~
+## ~
 
 ## Duration: ~30 minutes
 
@@ -24,6 +24,6 @@ basic.forever(() => {
 })
 ```
 
-### ~button /projects/light-monster/connect
+## ~button /projects/light-monster/connect
 NEXT: Connect
-### ~
+## ~

docs/projects/light-monster/connect.md

@@ -1,10 +1,10 @@
 # Connect
 
-### ~avatar avatar
+## ~avatar avatar
 
 Remote control your monster with another @boardname@
 
-### ~
+## ~
 
 ## Duration: ~30 minutes
 

docs/projects/light-monster/make.md

@@ -1,11 +1,11 @@
 # Make
-### @description Building the light monster
+## @description Building the light monster
 
-### ~avatar avatar
+## ~avatar avatar
 
 Turn a piece of coffee holders into a monster!
 
-### ~
+## ~
 
 ## Duration: ~60 minutes
 
@@ -20,6 +20,6 @@ Turn a piece of coffee holders into a monster!
 
 TODO
 
-### ~button /projects/coffee-cup-monster/code
+## ~button /projects/coffee-cup-monster/code
 NEXT: Code
-### ~
+## ~