Merge #782: Make psbt mod public and add required docs

34987d5 Make psbt mod public and add required docs (Steve Myers)

Pull request description:

  ### Description

  Make psbt mod public and add required docs. The module needs to be public so `bdk-ffi` can expose the new PSBT `fee_amount()` and `fee_rate()` functions.

  ### Notes to the reviewers

  I should have done this as part of #728.

  ### Changelog notice

  Make psbt module public to expose PsbtUtils trait to downstream projects.

  ### 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

  #### New Features:

  * [ ] I've added tests for the new feature
  * [x] I've added docs for the new feature

ACKs for top commit:
  rajarshimaitra:
    Concept + tACK 34987d5

Tree-SHA512: 99e91e948bccb7593a3da3ac5468232103d4ba90ad4e5888ef6aebb0d16511ad3a3286951779789c05587b4bb996bc359baa28b0f4c3c55e29b24bfc12a10073

Author: notmandatory

src/lib.rs

@@ -263,7 +263,7 @@ pub mod descriptor;
 #[cfg(feature = "test-md-docs")]
 mod doctest;
 pub mod keys;
-pub(crate) mod psbt;
+pub mod psbt;
 pub(crate) mod types;
 pub mod wallet;
 

src/psbt/mod.rs

@@ -9,11 +9,17 @@
 // You may not use this file except in accordance with one or both of these
 // licenses.
 
+//! Additional functions on the `rust-bitcoin` `PartiallySignedTransaction` structure.
+
 use crate::FeeRate;
 use bitcoin::util::psbt::PartiallySignedTransaction as Psbt;
 use bitcoin::TxOut;
 
+// TODO upstream the functions here to `rust-bitcoin`?
+
+/// Trait to add functions to extract utxos and calculate fees.
 pub trait PsbtUtils {
+    /// Get the `TxOut` for the specified input index, if it doesn't exist in the PSBT `None` is returned.
     fn get_utxo_for(&self, input_index: usize) -> Option<TxOut>;
 
     /// The total transaction fee amount, sum of input amounts minus sum of output amounts, in Sats.