receipts: decode token transfers and balance outputs from any receipt or logs array

[pkieltyka]

This PR allows you to pass in a txn hash or an array of logs, and it will output all token transfer details in terms of token/from/to/value, as well you can call .ComputeBalanceOutputs() on the token transfers and it will return the net values summing the combination of all events so you can see the balance of tokens for any account that happens in the transaction.

1. New receipts.FetchReceiptTokenTransfers(txnHash) method to fetch receipt and return TokenTransfers
2. new receipts.DecodeTokenTransfersFromLogs(logs) method to parse logs directly and return TokenTransfers
3. For any given TokenTransfers object, this is an array as []*TokenTransfer
4. A TokenTransfer is a struct of Token/From/To/Value
5. You can call tokenTransfers.ComputeBalanceOutputs() and it will return TokenBalances which is []*TokenBalance
6. TokenBalance is a struct that is Token/Account/Balance