Reorganize site to make room for documenting the other built-in modules.

doc/site/modules/core/class.markdown

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+^title Class Class
+
+**TODO**
+
+## Methods
+
+### **name**
+
+The name of the class.
+
+### **supertype**
+
+The superclass of this class.
+
+    :::wren
+    class Crustacean {}
+    class Crab is Crustacean {}
+
+    System.print(Crab.supertype) //> Crustacean
+
+A class with no explicit superclass implicitly inherits Object:
+
+    :::wren
+    System.print(Crustacean.supertype) //> Object
+
+Object forms the root of the class hierarchy and has no supertype:
+
+    :::wren
+    System.print(Object.supertype) //> null