1.2.0

• Breaking: POST /v1/swap takes send_amount instead of swap_fee_limit
  and accepts only a send_amount that buys exactly receive_amount.
  swap_fee_limit is gone from the swap state and the SDKs.
• Breaking: the SDK driver's quote pins either the amount to receive or
  the amount to send. The driver cannot restore swaps created before this
  release.

Minor

• The driver no longer fails a step when resending an observed, unconfirmed
  spend is refused, as when the chain source lags a block behind the node.
  The status stays Spending with the observed txid.
• LiquidEsplora keeps the transaction bodies it has fetched, so reading an
  address history costs one request per pass once its transactions are known,
  instead of one more per transaction.