BAU Windows 2.00 for BBC Master
            ===============================
  Original by Alan Blundell, BBC Acorn User July 1990
          Updated by J.G.Harston 31-Oct-2011

Commands
--------
  *WCLEAR clears any window data stored
  *WFREE displays remaining data space
  *WBACK makes the previous window active
  *WFORE makes the next window active

OSWORD interface
----------------
OSWORD 193 opens and closes windows.
  A=193, XY=>control block
  XY+0 Send length = 15+length of string at XY+14
  XY+1 Receive length = 4
  XY+2 Command code
  XY+3 Result code, set to 0 on entry
  XY+4 left
  XY+5 bottom
  XY+6 right
  XY+7 top
  XY+8 foreground colour
  XY+9 background colour
  XY+10 title bar foreground colour
  XY+11 title bar background colour
  XY+12 border foreground colour
  XY+13 border background colour
  XY+14... Title string, CR terminated

XY+4 to XY+7 specify the size of the text area. If
the window has a border it will occupy an area two
characters bigger all around. If it has an enclosed
title it will be two characters taller.

Command codes:
  0: CloseAll
  1: Close
  2: Release
  3: Open3: no title        no border      no background
  4: Open4: no title        no border
  5: Open5: top title       no border
  6: Open6: top title       square corners
  7: Open7: top title       round corners
  8: Open8: enclosed title  square corners
  9: Open9: enclosed title  round corners

Window styles:
    No title          Top title       Enclosed title
   +--------+        +Title----+        +--------+
   |        |        |         |        |Title   |
   |        |        |         |        +--------+
   |        |        |         |        |        |
   |        |        |         |        |        |
   |        |        |         |        |        |
   +--------+        +---------+        +--------+  

Errors
------
  128,No memory for window data
  129,Not suitable for teletext
  131,No window open
  132,Last window already active
  134,No window active
  135,Parameters