Added name/value paramter tuple to .save args

[LangleJ]

Ref https://developer.intuit.com/app/developer/qbo/docs/api/accounting/all-entities/purchase

From there ... "If a duplicate DocNumber needs to be supplied, add the query parameter name/value pair, include=allowduplicatedocnum to the URI. Sort order is ASC by default."

This pull allows a name/value pair to be passed through from save() to where the URI is formatted.

e.g. purchase.save(qb=client, parameter_tuple = ('include', 'allowduplicatedocnum'))