tr macros now documented

doc/tut2.txt

@@ -286,7 +286,7 @@ Procedures always use static dispatch. For dynamic dispatch replace the
 
 .. code-block:: nimrod
   type
-    TExpr = object ## abstract base class for an expression
+    TExpr = object of TObject ## abstract base class for an expression
     TLiteral = object of TExpr
       x: int
     TPlusExpr = object of TExpr
@@ -323,7 +323,7 @@ dispatching:
 .. code-block:: nimrod
 
   type
-    TThing = object
+    TThing = object of TObject
     TUnit = object of TThing
       x: int
       
@@ -702,3 +702,11 @@ regular expressions:
     return tkOperator
   else:
     return tkUnknown
+
+
+Term rewriting macros
+---------------------
+
+Term rewriting macros can be used to enhance the compilation process
+with user defined optimizations; see this `document <trmacros.html>`_ for 
+further information.