Merge bitcoindevkit/bdk-cli#305: Docs: Update README and changelog

Merge bitcoindevkit/bdk-cli#305: Docs: Update README and changelog

818505505f9297418dab9ae057178b93b63287b4 docs: Update README for Wallet API version (Vihiga Tyonum)
9437132c23ced7a634200a09154167f020027b9e docs: Update project changelog (Vihiga Tyonum)

Pull request description:

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  ### Description

  This PR updates the changelog to reflect the latest changes for v4.0 release and adds new features to the README.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

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