Add Ledger support
I would like to use vessel with my Ledger device storing my keys.
- Typescript library to communicate with Hive Ledger application: https://gitlab.com/engrave/ledger/ledger-app-hive
- Example implementation of CLI tool: https://gitlab.com/engrave/ledger/hive-ledger-cli
- Implementation of hiveledger.io: https://gitlab.com/engrave/ledger/hiveledger