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

doc/site/modules/core/bool.markdown

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+^title Bool Class
+
+Boolean [values][]. There are two instances, `true` and `false`.
+
+[values]: ../../values.html
+
+## Methods
+
+### **!** operator
+
+Returns the logical complement of the value.
+
+    :::wren
+    System.print(!true) //> false
+    System.print(!false) //> true
+
+### toString
+
+The string representation of the value, either `"true"` or `"false"`.