chain: add Transaction::hash() method.

This makes Transaction and Block have a consistent API.

zebra-chain/src/block.rs

@@ -50,7 +50,7 @@ impl Block {
             })
     }
 
-    /// Get the hash for the current block
+    /// Compute the hash of this block.
     pub fn hash(&self) -> Hash {
         Hash::from(self)
     }

zebra-chain/src/transaction.rs

@@ -97,6 +97,11 @@ pub enum Transaction {
 }
 
 impl Transaction {
+    /// Compute the hash of this transaction.
+    pub fn hash(&self) -> Hash {
+        Hash::from(self)
+    }
+
     /// Access the transparent inputs of this transaction, regardless of version.
     pub fn inputs(&self) -> &[transparent::Input] {
         match self {

zebra-chain/src/transaction/hash.rs

@@ -17,8 +17,8 @@ use super::Transaction;
 #[cfg_attr(test, derive(Arbitrary))]
 pub struct Hash(pub [u8; 32]);
 
-impl From<Transaction> for Hash {
-    fn from(transaction: Transaction) -> Self {
+impl<'a> From<&'a Transaction> for Hash {
+    fn from(transaction: &'a Transaction) -> Self {
         let mut hash_writer = sha256d::Writer::default();
         transaction
             .zcash_serialize(&mut hash_writer)