1437e1ecfe Add the hardware_signer example (Daniela Brozzoni)
1a71eb1f47 Update the hardwaresigner module documentation (Daniela Brozzoni)
0695e9fb3e Bump HWI to 0.2.3 (Daniela Brozzoni)
a4a43ea860 Re-export HWI if the hardware-signer feature is set (Daniela Brozzoni)
Pull request description:
### Description
### Notes to the reviewers
### Changelog notice
- bdk re-exports the `hwi` create when the feature `hardware-signer` is on
- Add `examples/hardware_signer.rs`
### Checklists
#### All Submissions:
* [x] I've signed all my commits
* [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
* [x] I ran `cargo fmt` and `cargo clippy` before committing
ACKs for top commit:
afilini:
ACK 1437e1ecfe
Tree-SHA512: 181f4d14dce11e19497fbf30e0af8de21c2c210d37129d7d879ed5670ed09a25be1c8d371389c431e18df9e76870cf5e4afe7b29a6c05fe59b3e1816bc8cf673