Rescales the font being used on the current drawing surface.
The scaling involves integer truncation and so is only approximate. A more accurate result
may be given by SCALE_FONT1@. This routine uses rounding rather than truncation but is otherwise
the same as SCALE_FONT@.
Because of their approximate nature, these functions should not be used in succession and it is
recommended that a routine such as SIZE_IN_PIXELS@ be used from time to time in order to set a base size.
Alternatively the subroutine UNSCALE_FONT@(), which takes no arguments, may be called in order to undo
the immediately previous call to SCALE_FONT@ or SCALE_FONT1@.