message: Address Daira's review comments
diff: @@ -87,13 +87,14 @@ impl<Node: Hashable> CommitmentTree<Node> {
  })
  }
  - /// Returns the number of notes in the tree.
  + /// Returns the number of leaf nodes in the tree.
  pub fn size(&self) -> usize {
  self.parents.iter().enumerate().fold(
  match (self.left, self.right) {
  (None, None) => 0,
  - (Some(_), None) | (None, Some(_)) => 1,
  + (Some(_), None) => 1,
  (Some(_), Some(_)) => 2,
  + (None, Some(_)) => unreachable!(),
  },
  |acc, (i, p)| {
  // Treat occupation of parents array as a binary number
  @@ -110,7 +111,7 @@ impl<Node: Hashable> CommitmentTree<Node> {
  && self.parents.iter().all(|p| p.is_some())
  }
  - /// Adds a note to the tree.
  + /// Adds a leaf node to the tree.
  ///
  /// Returns an error if the tree is full.
  pub fn append(&mut self, node: Node) -> Result<(), ()> {
  @@ -269,7 +270,7 @@ impl<Node: Hashable> IncrementalWitness<Node> {
  Optional::write(&mut writer, &self.cursor, |w, t| t.write(w))
  }
  - /// Returns the position of the witnessed note in the commitment tree.
  + /// Returns the position of the witnessed leaf node in the commitment tree.
  pub fn position(&self) -> usize {
  self.tree.size() - 1
  }
  @@ -328,7 +329,7 @@ impl<Node: Hashable> IncrementalWitness<Node> {
  d + skip
  }
  - /// Tracks a note that has been added to the underlying tree.
  + /// Tracks a leaf node that has been added to the underlying tree.
  ///
  /// Returns an error if the tree is full.
  pub fn append(&mut self, node: Node) -> Result<(), ()> {
  