Update simpleCart.js

Add SendForm options to allow item formatting setting index start. 

Ex used for mvc model binder:
    type: "SendForm",
    itemFormat: 'items[{index}].{name}',
    indexStart: 0

Results in:
  items[0].name
  items[0].quantity
  items[0].price
  items[0].options
  items[1].name
  items[1].quantity
  items[1].price
  items[1].options
  ...etc