c34d5f8f85 Implement PartiallySignedTransaction::fee (hashmap)
Pull request description:
to calculate fee if previous outputs are available.
Closes https://github.com/rust-bitcoin/rust-bitcoin/issues/1220
ACKs for top commit:
Kixunil:
ACK c34d5f8f85 if CI passes
tcharding:
ACK c34d5f8f85
apoelstra:
ACK c34d5f8f85
Tree-SHA512: 697b837de2fb21bbd5d489c524c06a56bb35b73c0f32cc5b0500f5508f3c539b21d327cd556a04ee847ccf8d98829da994d90c19e80c457ddba2cd9d3469476e