scale
Description:
Changes the transformation represented by this to be the transformation given by first scaling by sx
       in the X direction and sy in the Y direction then applying the original transformation.
Parameters:
| this | 
           a `PangoMatrix`  | 
      
| scale_x | 
           amount to scale by in X direction  | 
      
| scale_y | 
           amount to scale by in Y direction  |