• Transaction changes
• Important tef* and tel* and errors will no longer be presented as
  final. Rather than considering these errors final, ripple-lib will wait until
  the LastLedgerSequence specified in the transaction is exceeded. This makes
  failures more definitive, and ensures that no transaction will resubmit
  indefinitely.
• A new, final tej-class error is introduced to account for transactions that
  are locally determined to have expired: tejMaxLedger.
• Allow per transaction fees to be set, transaction.setFixedFee()
• Improve memo support
  • Add MemoFormat property for memo
  • Enforce MemoFormat and MemoType to be valid ASCII
  • Support text and json MemoFormat
• Update jscl library
  • Improved entropy by taking advantage of platform crypto
  • Use jscl's k256 curve instead of altering the c256 curve with k256 configuration
  • deprecated: the c256 curve is linked to the k256 curve to provide backwards compatibility, this link will be removed in the future