Get full balance from an address and send funds from that address
I have an address with a payment ID and I want to see the current balance of that address. Do I need to add all incoming transactions, or is there a way to directly get the balance?

Another question is that I would like to send the funds from an address. Say, I want to empty an address that received a transaction. How can this be done? Right now, I am only able to send transactions from my wallet, but I am not able to select which funds I want to spend. 

Also, can I use a payment_id to "label" an outgoing transaction?

Thank you for maintaining this library.