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
darn...seems strange for it to accept string and symbol. I usually see that in code where the real data is strings but devs write tests using symbols.