New qs version

The old `qs` version could not handle parameters like `isVatExampt=1`. It would simply stringify it to `&isVatExempt`, without any value.

add and remove custom charges

fix bad parameter name in addCustomCharge

fix editSubscription

Update README.md

bump version for npm release

new better tests and fixed add and remove item without amount

whoops package.json missing a comma

update package.json for publish