The points in this file aren't definitive TODOs:
They are an attempt to make the names of things better match their current
meaning. But changing names always has side-effects that have to be taken
into consideration before planning to actually do so.

 - Rename MathCell to Cell? It has grown to be the base class of all cells,
   not only for math ones.
 - Rename MathCtrl to something like Canvas or Worksheet? This file doesn't
   control only math stuff any more. But it represents the canvas containing
   the work sheet.
   
 - Can the Destructor of the *Cell classes be reduced to a call to
   Destroy()?
