Feature/beta marketplace api

Adds support for PIN's beta Marketplace Payouts API - https://pin.net.au/docs/guides/marketplace-payouts

https://pin.net.au/docs/api/transfers
https://pin.net.au/docs/api/recipients
https://pin.net.au/docs/api/recipients
https://pin.net.au/docs/api/balance
https://pin.net.au/docs/api/bank-accounts
it comes from the server in the form of string, it comes from the user in form of symbol or string (you build a hash you're more likely to use symbols than strings).  I guess I could just stringify keys too and check then.