add the percentage utility
add the discountable module
add the taggable module
add the tag model
add the product model
add the pack model
add the mixed pack model
add the discount model
add the cart item model
add the tally model
add the cart model
add the interpretable module
add the discountable interpreter
add the taggable interpreter
add the money interpreter
add the percentage interpreter
add the product interpreter
add the savings interpreter
add the packable interpreter
add the mixed pack interpreter