This commit updates the rust-toolchain to the current stable version
1.59, and fixes a number of new clippy warnings from that change.
Other changes:
- updates backoff to 0.4
- updates swap to 2021 edition
- updates comfy-table to 5.0
- updates monero-wallet to 2021 edition
- updates moneor-harness to 2021 edition
- updates bdk and rust_decimal
- updates tokio-util to 0.7
- updates workflow to use actions/setup-python@3
- updates pem and serde_with
- adds stable rust toolchain notice to readme
This is fairly bare-bones for now and only contains one piece of
functionality: choosing random key offsets.
More functionality for actually signing Monero transactions will
be added later.
