Implement AsRef<[u8]> and into_bytes(self) for Unparsed

Add conversion methods to gain access to the inner bytes of `Unparsed`,
per discussion in #72

Signed-off-by: Ross Williams <ross@ross-williams.net>

Author: overhacked

src/proto/message/unparsed.rs

@@ -16,6 +16,11 @@ impl Unparsed {
         let mut v = &self.0[..];
         T::decode(&mut v)
     }
+
+    /// Obtain the unparsed bytes as a `Vec<u8>`, consuming the `Unparsed`
+    pub fn into_bytes(self) -> Vec<u8> {
+        self.0
+    }
 }
 
 impl From<Vec<u8>> for Unparsed {
@@ -24,6 +29,12 @@ impl From<Vec<u8>> for Unparsed {
     }
 }
 
+impl AsRef<[u8]> for Unparsed {
+    fn as_ref(&self) -> &[u8] {
+        self.0.as_ref()
+    }
+}
+
 impl Encode for Unparsed {
     fn encoded_len(&self) -> ssh_encoding::Result<usize> {
         Ok(self.0.len())