Merge bitcoindevkit/bdk#1001: Rename "keychanins" to keychains

22b8a4884245449fcf60877ca031e0e9e7495de9 Rename "keychanins" to keychains (Daniela Brozzoni)

Pull request description:

  ### 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:
  notmandatory:
    ACK 22b8a4884245449fcf60877ca031e0e9e7495de9

Tree-SHA512: 13ebbd597771a9d91c317fedc4dc506a275a641b764f24650cd13217cf8ac0d06c42a935a8c9e1e7f4761d2ade473c7f8381e90875e867b7a61381aa33cd8581