Optimize Witness Serialization

fix #942

src/blockdata/witness.rs

@@ -13,6 +13,8 @@ use crate::VarInt;
 
 #[cfg(feature = "serde")]
 use serde;
+use serde::ser::SerializeSeq;
+
 
 /// The Witness is the data used to unlock bitcoins since the [segwit upgrade](https://github.com/bitcoin/bips/blob/master/bip-0143.mediawiki)
 ///
@@ -282,8 +284,13 @@ impl serde::Serialize for Witness {
     where
         S: serde::Serializer,
     {
-        let vec: Vec<_> = self.to_vec();
-        serde::Serialize::serialize(&vec, serializer)
+        let mut seq = serializer.serialize_seq(Some(self.witness_elements))?;
+
+        for elem in self.iter() {
+            seq.serialize_element(&elem)?;
+        }
+
+        seq.end()
     }
 }
 #[cfg(feature = "serde")]