Adding Extra Inputs to the ProcPrim

1. Decide upon names for the new inputs.
    ex. min_circumference
        max_circumference
        
2. Modify the struct. Example:
        RtFloat min_circumference;
        RtFloat max_circumference;
        
3. Modify the sscanf(). For example:
   Add extra %f or %d
   and then add/edit,
        dataPtr->min_circumference, 
        &dataPtr->max_circumference,

4. In the Subdivide() function grab
   local copies of the values of the
   new inputs. For example:
        RtFloat min_circum = ((SpheresData*)data)->min_circumference;
        RtFloat max_circum = ((SpheresData*)data)->max_circumference;

5. Use the new values in some meaningful
   way. For example:
        RtFloat circum = randBetween(min_circum, max_circum);
        RiSphere(radius, -radius, radius, circum, RI_NULL);