operator: to-category

    description:
        to-category |x>
        append the coefficient of the ket, to the ket label
            
    examples:
        to-category 57| >
            |57>
      
        to-category |age>
            |age: 1>
        
        to-category 23|age>
            |age: 23>
        
    see also:
        to-value, push-float, pop-float