Changes to rest_api (#480)

* Add half-finished rest api changes

* Add basic, messy changes to rest api

* Fix expect() in ApiRequest

* Remove ApiRequest, add route for beacon state

* Tidy rest api, add get state from root

* Add api method for getting state roots by slot

* Add test for URL helper

* Simplify state_at_slot fn

* Add tests for rest api helper fns

* Add extra tests for parse root

* Fix clippy lints

* Fix compile error in rest api

* Update test to new ethereum-types

beacon_node/store/src/iter.rs

@@ -24,6 +24,15 @@ impl<'a, U: Store, E: EthSpec> AncestorIter<U, BlockRootsIterator<'a, E, U>> for
     }
 }
 
+impl<'a, U: Store, E: EthSpec> AncestorIter<U, StateRootsIterator<'a, E, U>> for BeaconState<E> {
+    /// Iterates across all the prior state roots of `self`, starting at the most recent and ending
+    /// at genesis.
+    fn try_iter_ancestor_roots(&self, store: Arc<U>) -> Option<StateRootsIterator<'a, E, U>> {
+        // The `self.clone()` here is wasteful.
+        Some(StateRootsIterator::owned(store, self.clone(), self.slot))
+    }
+}
+
 #[derive(Clone)]
 pub struct StateRootsIterator<'a, T: EthSpec, U> {
     store: Arc<U>,