SETGAUGE expression , expression , expression
    
   Synopsis:
      Updates a 'main' window gauge
    
   Notes:
      Updates a gauge that was added to the 'main' window with an ADDGAUGE or
         ADDCONGAUGE statement.
      The first expression is the gauge's unique number. If the gauge doesn't 
         exist, the SETGAUGE statement is ignored, but the number isn't an 
         integer, 0 or above, you'll see an error message.
      The second and third expressions should evaluate to numbers used to set
         the length of the "full" and "empty" portions of the gauge. Any decimal 
         number is acceptable, even negative numbers. If these expressions don't 
         evaluate to a number, the gauge is blanked.
      After an ADDGAUGE statement, the first number is expected (but not
         required) to be less than or equal to the second one. After an 
         ADDCONGAUGE statement, the sum of the two numbers is expected (but not
         required) to be constant, at least in the short term.

   Requires:
      If the script is not being run as a task, the SETGAUGE statement is
         ignored (and no error message is generated). Execution continues with
         the next statement.
         
   Examples:
      ! Character's health points are at 50%
      ADDGAUGE 1, "HP", "RED", "red", "WHITE"
      SETGAUGE 1, 50, 100

      ! Character's energy points are very low
      ADDGAUGE 2, "EP", "GREEN", "green", "black"
      SETGAUGE 2, 0.017, 1

      ! Show a gauge where the two numbers are added
      ! Character has 900xp, and needs 100 more to level up
      ADDCONGAUGE 3, "XP", "MAGENTA", "magenta", "WHITE"
      SETGAUGE 3, 900, 100
