[TASK] update sjcl

- native support for k256
- improved entropy by taking advantage of platform crypto

- remove unnecessary sjcl overrides from sjcl-secp256k1.js
- updated ripple-lib curve instantiations to use k256
- add curve override so c256 points to k256

https://github.com/bitwiseshiftleft/sjcl/commit/16dde36fa2a58845f639429acd5bc4e4ebb5a0f1
Merge pull request #220 from geertweening/update_sjcl

[TASK] update sjcl
Cleanup

- Deprecate 'save' event
- Add TransactionQueue.getMinLedger(), use this as ledger_index_min
  in account_tx request on reconnect
- tx.sign() no longer accepts a callback
- Add various setters and jsdoc to transaction.js
- Normalize setters, e.g. sourceTag() and destinationTag()
- Minor optimization in call to tx.hash() in TransactionManager prior
  to submit; allow `serialized` argument to tx.hash() such that the
  transaction is not serialized twice
Make LastLedgerSequence offset configurable, default to 3
Do not bump LastLedgerSequence on resubmit
Rework tef and tel-class transaction error handling

Do not finalize tef or tel-class errors until LastLedgerSequence is
exceeded. Transactions that fail in this way will now be aborted
with a tej-class error. Errors like tefALREADY and tefMAX_LEDGER
should now be opaque to the user and have no consequence in
determining a final state.
Merge pull request #221 from ripple/transaction-updates

Transaction updates
[FEATURE] allow per transaction fees to be set
Merge pull request #222 from boxbag/transaction-set-fee

[FEATURE] allow per transaction fees to be set
[FEATURE] improve memo support

- add MemoFormat property for memo
- MemoFormat and MemoType must be valid ASCII
- Memo content is converted on the serialization level
- add parsed_* version of Memo content if the parser understand the format
- support `text` and `json` MemoFormat

[FIX] double serialization overriding Memo contents

The copy made in from_json wasn't a deep copy
Merge pull request #223 from geertweening/feature/memo_format_type

[FEATURE] improve memo support
[DOC] update release notes