User initiated payments

[JulianTosh]

This is somewhat dependant on issue #8Setanameforcreatedpayments.

Merchants should be able to provide a general public link to create their own payment invoice with the ability to add specific details of their payment as provided by Issue #8. An API might even allow the merchant to add in specific, optional information for the patron like an amount, product ID, contact info, etc.

This could be used like BitPay/MTGOX merchant checkout/payment buttons.