Add digest subtypes and update dependencies (#2734)

* Add different digest types for different parts of the code

* Add script to update dependencies

* Remove an old changelog

* `Inherent` → `PreRuntime`

substrate/scripts/update-deps.sh

@@ -0,0 +1,9 @@
+#!/bin/sh --
+set -eu
+case $0 in
+   (/*) dir=${0%/*}/;;
+   (*/*) dir=./${0%/*};;
+   (*) dir=.;;
+esac
+
+find "$dir/.." -name Cargo.lock -execdir cargo update \;