Light friendly storage tracking: changes trie + extending over ranges (#628)

* changes_trie

* changs_trie: continue

* changes_trie: adding tests

* fixed TODO

* removed obsolete ExtrinsicChanges

* encodable ChangesTrieConfiguration

* removed polkadot fle

* fixed grumbles

* ext_storage_changes_root returns u32

* moved changes trie root to digest

* removed commented code

* read storage values from native code

* fixed grumbles

* fixed grumbles

* missing comma

substrate/core/primitives/src/changes_trie.rs

@@ -0,0 +1,30 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Substrate changes trie configuration.
+
+/// Substrate changes trie configuration.
+#[cfg_attr(any(feature = "std", test), derive(Serialize, Deserialize))]
+#[derive(Debug, Clone, PartialEq, Eq, Default, Encode, Decode)]
+pub struct ChangesTrieConfiguration {
+	/// Interval (in blocks) at which level1-digests are created. Digests are not
+	/// created when this is less or equal to 1.
+	pub digest_interval: u64,
+	/// Maximal number of digest levels in hierarchy. 0 means that digests are not
+	/// created at all (even level1 digests). 1 means only level1-digests are created.
+	/// 2 means that every digest_interval^2 there will be a level2-digest, and so on.
+	pub digest_levels: u32,
+}