MultiLevel_Undo
Author: Rainer Kowallik


Purpose: Support multi level Undo / Redo for tkedit
         Additionally add an "Overstrike" mode to tkedit (may sound strange at
         this point, but for technical reasons this was a good place to add
         this feature)

This macro adds the following entries to the "Edit" menu:

   Edit/MultiLevel Undo    reverses the last single action
   Edit/MultiLevel Redo    restores the last undone action
   
   and one other Entry to the Preferences Menu:
   
   Preferences/Copy UndoBuffer
                           Saves the UndoBuffer at "SyncText" to be able
                           to restore after a "Limited Undo".
                           This needs of course some memory...
                           And some time...
                           And it is not tested extensively...
                           And it is disabled by default !
   
The MultiLevel "Undo" is bound to [ctrl-shift-U]
   
The "Limited Undo" is still available ([ctrl-u]) and does a slightly different
thing. You can in general mix usage of both Undo functions. This is especially
usefull when restoring from an automated repetition function.
The "Limited Undo" brings you to the text as it was before the repetition
function was called, whereas the "Multilevel Undo" brings you back step by
step.
   
Restrictions:
   The maximum of available Undo levels is set to 100 by default

Variables for External use:
   MaxUndo        Number of available Undo levels
   MaxRedo        Number of available Redo Levels
         
-------------------------------------------------------------------------------
Rainer Kowallik             postdoc at       DESY-IfH Zeuthen (Germany)
Email: kowallik@ifh.de                       Platanenallee 6, D-15738 Zeuthen
