fixed and documented computedGoto pragma

doc/manual.txt

@@ -4561,6 +4561,51 @@ tested against via linear scanning. If put into the last branch of the
 whole ``case`` statement, the whole ``case`` statement uses linear scanning.
 
 
+computedGoto pragma
+-------------------
+The `computedGoto`:idx: pragma can be used to tell the compiler how to 
+compile a Nimrod `case`:idx: in a ``while true`` statement. 
+Syntactically it has to be used as a statement inside the loop:
+
+.. code-block:: nimrod
+
+  type
+    MyEnum = enum
+      enumA, enumB, enumC, enumD, enumE
+
+  proc vm() =
+    var instructions: array [0..100, MyEnum]
+    instructions[2] = enumC
+    instructions[3] = enumD
+    instructions[4] = enumA
+    instructions[5] = enumD
+    instructions[6] = enumC
+    instructions[7] = enumA
+    instructions[8] = enumB
+
+    instructions[12] = enumE
+    var pc = 0
+    while true:
+      {.computedGoto.}
+      let instr = instructions[pc]
+      case instr
+      of enumA:
+        echo "yeah A"
+      of enumC, enumD:
+        echo "yeah CD"
+      of enumB:
+        echo "yeah B"
+      of enumE:
+        break
+      inc(pc)
+    
+  vm()
+
+As the example shows ``computedGoto`` is mostly useful for interpreters. If
+the underlying backend (C compiler) does not support the computed goto 
+extension the pragma is simply ignored.
+
+
 unroll pragma
 -------------
 The `unroll`:idx: pragma can be used to tell the compiler that it should unroll

doc/nimrodc.txt

@@ -488,7 +488,7 @@ in C/C++).
 
 
 Nimrod idetools integration
-=======================
+===========================
 
 Nimrod provides language integration with external IDEs through the
 idetools command. See the documentation of `idetools <idetools.html>`_