Add as_bytes and to_bytes functions

As discussed and implemented in `rust-bitcoin` PR #2585 its useful to
get a byte slice as well as the already provided method for a array
reference. Also, if "alloc" feature is enabled its useful to be able to
get a vector.

src/hmac.rs

@@ -72,6 +72,13 @@ impl<const N: usize> Hmac<N> {
     /// Returns a reference to the underlying byte array.
     pub fn as_byte_array(&self) -> &[u8; N] { &self.0 }
 
+    /// Returns a reference to the underlying byte array as a slice.
+    pub fn as_bytes(&self) -> &[u8] { &self.0 }
+
+    /// Copies the underlying bytes into a new `Vec`.
+    #[cfg(feature = "alloc")]
+    pub fn to_bytes(&self) -> Vec<u8> { self.0.to_vec() }
+
     /// Returns an all zero hash.
     ///
     /// An all zeros hash is a made up construct because there is not a known input that can

src/internal_macros.rs

@@ -206,6 +206,15 @@ macro_rules! hash_type {
             /// Returns a reference to the underlying byte array.
             pub fn as_byte_array(&self) -> &[u8; $bits / 8] { &self.0 }
 
+            /// Returns a reference to the underlying byte array as a slice.
+            #[inline]
+            pub fn as_bytes(&self) -> &[u8] { &self.0 }
+
+            /// Copies the underlying bytes into a new `Vec`.
+            #[cfg(feature = "alloc")]
+            #[inline]
+            pub fn to_bytes(&self) -> Vec<u8> { self.0.to_vec() }
+
             /// Returns an all zero hash.
             ///
             /// An all zeros hash is a made up construct because there is not a known input that can

src/sha256t.rs

@@ -113,6 +113,13 @@ impl<T: Tag> Hash<T> {
     /// Returns a reference to the underlying byte array.
     pub fn as_byte_array(&self) -> &[u8; 32] { &self.0 }
 
+    /// Returns a reference to the underlying byte array as a slice.
+    pub fn as_bytes(&self) -> &[u8] { &self.0 }
+
+    /// Copies the underlying bytes into a new `Vec`.
+    #[cfg(feature = "alloc")]
+    pub fn to_bytes(&self) -> Vec<u8> { self.0.to_vec() }
+
     /// Returns an all zero hash.
     ///
     /// An all zeros hash is a made up construct because there is not a known input that can