Style example output and errors in the docs.

doc/site/core/class.markdown

@@ -15,14 +15,14 @@ The superclass of this class.
     class Crustacean {}
     class Crab is Crustacean {}
 
-    System.print(Crab.supertype) // "Crustacean".
+    System.print(Crab.supertype) //> Crustacean
 
 A class with no explicit superclass implicitly inherits Object:
 
     :::wren
-    System.print(Crustacean.supertype) // "Object".
+    System.print(Crustacean.supertype) //> Object
 
 Object forms the root of the class hierarchy and has no supertype:
 
     :::wren
-    System.print(Object.supertype) // "null".
+    System.print(Object.supertype) //> null