Fee as type Coins instead of Coin

[rigelrozanski]

Why should the fee only be one coin, maybe there are multiple types of coins that could be sent as a fee? If the transaction is already provisioning the type of coin the validator is going to need to be making complex value judgements between currencies, so why not?

[rigelrozanski]

Additionally, this will allow us to send true fee-less transactions because the type coin is always initialized with something, aka var fee types.coin has the default value of {"",0} built in, which creates problems if you don't want to send in coins of the type "" with your transaction.

• The other option is to modify the validity checks to ignore a coin type if the amount is zero