added docs for discount codes, sales and carts
added docs for discount codes, sales and carts

traxxas/cartridge,ryneeverett/cartridge,Parisson/cartridge,traxxas/cartridge,viaregio/cartridge,wyzex/cartridge,wbtuomela/cartridge,syaiful6/cartridge,traxxas/cartridge,Kniyl/cartridge,Parisson/cartridge,stephenmcd/cartridge,dsanders11/cartridge,stephenmcd/cartridge,jaywink/cartridge-reservable,viaregio/cartridge,dsanders11/cartridge,jaywink/cartridge-reservable,dsanders11/cartridge,wbtuomela/cartridge,Kniyl/cartridge,ryneeverett/cartridge,wyzex/cartridge,syaiful6/cartridge,Parisson/cartridge,jaywink/cartridge-reservable,ryneeverett/cartridge,Kniyl/cartridge,stephenmcd/cartridge,syaiful6/cartridge,wyzex/cartridge,wbtuomela/cartridge