implemented marker procs for the GC resulting in huge speedups

lib/system/hti.nim

@@ -60,6 +60,7 @@ type # This should be he same as ast.TTypeKind
     base: ptr TNimType
     node: ptr TNimNode # valid for tyRecord, tyObject, tyTuple, tyEnum
     finalizer: pointer # the finalizer for the type
+    marker: proc (p: pointer, op: int) # marker proc for GC
   PNimType = ptr TNimType
   
 # node.len may be the ``first`` element of a set