This sample shows how to create a user interface with xbw:
add or subtract two numbers, depending on the value of a control
variable ("A" or "S"). Display the result on the user interface.
These operations are executed by an application program, not by xbw
itself. 

Features:
=========
- addermfx.h contains a description of I/O Variables that are exchanged 
  between xbw and the application program (adder and adder.c, rsp.)
- adderwdw.mta is an automatically created user interface; it is
  created by the program "makemfx"
- startadder.mta is a handmade version; handmade corrections were
  necessary for a nicer layout and a second "start" button for adder.c
  The two "start" buttons handle the "+" and "-" operations.

