Update SSZ

- Implement generic list decoding>
- Expose `encode` mod.
- Add convenience encoding function.

beacon_chain/utils/ssz/src/impl_decode.rs

@@ -1,4 +1,5 @@
 use super::ethereum_types::H256;
+use super::decode::decode_ssz_list;
 use super::{
     DecodeError,
     Decodable,
@@ -65,6 +66,16 @@ impl Decodable for H256 {
     }
 }
 
+impl<T> Decodable for Vec<T>
+    where T: Decodable
+{
+    fn ssz_decode(bytes: &[u8], index: usize)
+        -> Result<(Self, usize), DecodeError>
+    {
+        decode_ssz_list(bytes, index)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;