Issuing and Exchange functions

Function definitions
Both functions are to be called on the Cash contract.

Request issue of Verified cash token for fiat paid in

payIn(_tokens, _payer, _currency)
Function parameter
number of cash tokens to issue
address of user paying in fiat currency
name of fiat currency paid in

Request exchange of Verified cash tokens

transferFrom(_fromCurrency, _toCurrency, _amount)
Function parameter
address of Verified cash token to debit and convert from
address of Verified cash token to exchange to and credit
name of the cash tokens to debit and convert