Added historical summaries to Capella beacon state.

In Capella, historical_roots has been replaced by historical_summaries, but this was not reflected in our state object.

Fixes #315

types/capella/historical_summary.yaml

@@ -0,0 +1,9 @@
+Capella:
+  HistoricalSummary:
+    type: object
+    description:  "The [`HistoricalSummary`](https://github.com/ethereum/consensus-specs/blob/v1.3.0/specs/capella/beacon-chain.md#historicalsummary) object from the CL Capella spec."
+    properties:
+      block_summary_root:
+        $ref: '../primitive.yaml#/Root'
+      state_summary_root:
+        $ref: '../primitive.yaml#/Root'

types/capella/state.yaml

@@ -25,7 +25,7 @@ Capella:
           $ref: '../primitive.yaml#/Root'
       historical_roots:
         type: array
-        description: "Variable length list, maximum 16777216 items"
+        description: "Variable length list, maximum 16777216 items. Frozen in Capella, replaced by historical_summaries."
         items:
           $ref: '../primitive.yaml#/Root'
       eth1_data:
@@ -86,3 +86,8 @@ Capella:
         $ref: "../primitive.yaml#/Uint64"
       next_withdrawal_validator_index:
         $ref: "../primitive.yaml#/Uint64"
+      historical_summaries:
+          type: array
+          items:
+            $ref: "./historical_summary.yaml#/Capella/HistoricalSummary"
+          description: "Variable length list, maximum 16777216 items"