
plstransform: Set a global coordinate transform function 

DESCRIPTION:

    This function is used in example 19. 

SYNOPSIS:

plstransform(transform_fun, data)

ARGUMENTS:

    transform_fun (void (*) (PLFLT, PLFLT, PLFLT*, PLFLT*, PLPointer) ,
    input) :    Pointer to a function that defines a transformation
    from the input (x, y) coordinate to a new plot world coordiante. 

    data (PLPointer, input) :     Optional extra data for 
    transform_fun. 
