Merge #863: Rename secret_bytes to to_secret_bytes

fc269ee Rename secret_bytes to to_secret_bytes (Tobin C. Harding)

Pull request description:

  As we did elsewhere add a new function and deprecate the old one.
  
  Done for the two places we missed:
  
  - `ecdh::SharedSecret`
  - `Keypair`
  
  Close: #845


ACKs for top commit:
  apoelstra:
    ACK fc269ee; successfully ran local tests


Tree-SHA512: a9a374978c2f5a6d37464acd3c00e5e9487f30f07987c9e69e39cf4419ce85fbc39f4c5e03d42abdec25356d143f9bfcf3944e024cd6f804a7a3afb468cee76d

Author: apoelstra

src/ecdh.rs

@@ -55,7 +55,12 @@ impl SharedSecret {
 
     /// Returns the shared secret as a byte value.
     #[inline]
-    pub fn secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] { self.0 }
+    pub fn to_secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] { self.0 }
+
+    /// Returns the shared secret as a byte value.
+    #[deprecated(since = "TBD", note = "Use `to_secret_bytes` instead.")]
+    #[inline]
+    pub fn secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] { self.to_secret_bytes() }
 
     /// Creates a shared secret from `bytes` array.
     #[inline]

src/key/mod.rs

@@ -612,10 +612,15 @@ impl Keypair {
 
     /// Returns the secret bytes for this key pair.
     #[inline]
-    pub fn secret_bytes(&self) -> [u8; constants::SECRET_KEY_SIZE] {
+    pub fn to_secret_bytes(&self) -> [u8; constants::SECRET_KEY_SIZE] {
         *SecretKey::from_keypair(self).as_ref()
     }
 
+    /// Returns the secret bytes for this key pair.
+    #[deprecated(since = "TBD", note = "use to_secret_bytes instead")]
+    #[inline]
+    pub fn secret_bytes(&self) -> [u8; constants::SECRET_KEY_SIZE] { self.to_secret_bytes() }
+
     /// Tweaks a keypair by first converting the public key to an xonly key and tweaking it.
     ///
     /// # Errors