circuit transfer fees

[barryWhiteHat]

Allow fees to be taken based upon the transfer. The operator create teh fee tree and passes it as a public input from the smart contract

1. Add a fee value to the signtuare

2. Subtract sig.amount from the sender leaf

3. Add sig.amount - sig.fee to the recipient leaf (be careful about overflows)

4. For each transaction the operator maintins a fee tree. With 8 layer.

5. Orginally each leaf is zero.

6. The oeprator can either add a leaf to that tree that represents a single fee in a token.
   or

7. add fee to the balance of a leaf in that tree as long as it has the same token type.

8. This is passed as a public input to the snark.

9. Confirm that the final fee tree == the public input fee tree

10. Add smart contract functionality to allow the operator to withdraw these funds.

[barryWhiteHat]

Lets replace the fee tree with #8 where we can store the fee and the token.

[therealyingtong]

it seems to make more sense to only allow one token type. otherwise we would need a fee leaf for each token type.

[barryWhiteHat]

So what i was thinking was to include hte fee in the transfer digest and use the smart contract to pay that fee to each operator. We can also use a snark to merge these together to save gas.