update the gemspec
change the spec helper from rails to the checkbot gem
add the money utility
update the money utility with arithmetic methods
add the percentage utility
add the optional regexp utilitiy
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