superstruct the AttesterSlashing (#5636)

* `superstruct` Attester Fork Variants

* Push a little further

* Deal with Encode / Decode of AttesterSlashing

* not so sure about this..

* Stop Encode/Decode Bounds from Propagating Out

* Tons of Changes..

* More Conversions to AttestationRef

* Add AsReference trait (#15)

* Add AsReference trait

* Fix some snafus

* Got it Compiling! :D

* Got Tests Building

* Get beacon chain tests compiling

---------

Co-authored-by: Michael Sproul <micsproul@gmail.com>

lcli/src/indexed_attestations.rs

@@ -35,7 +35,7 @@ pub fn run<E: EthSpec>(matches: &ArgMatches) -> Result<(), String> {
         .into_iter()
         .map(|att| {
             let committee = state.get_beacon_committee(att.data().slot, att.data().index)?;
-            get_indexed_attestation(committee.committee, &att)
+            get_indexed_attestation(committee.committee, att.to_ref())
         })
         .collect::<Result<Vec<_>, _>>()
         .map_err(|e| format!("Error constructing indexed attestation: {:?}", e))?;

lcli/src/transition_blocks.rs

@@ -390,7 +390,7 @@ fn do_transition<E: EthSpec>(
         // Signature verification should prime the indexed attestation cache.
         assert_eq!(
             ctxt.num_cached_indexed_attestations(),
-            block.message().body().attestations().len()
+            block.message().body().attestations_len()
         );
     }