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/srml/example/src/lib.rs

@@ -326,9 +326,10 @@ mod tests {
 	use super::*;
 
 	use runtime_io::with_externalities;
-	use substrate_primitives::{H256, Blake2Hasher};
+	use substrate_primitives::{H256, Blake2Hasher, RlpCodec};
 	use runtime_primitives::BuildStorage;
 	use runtime_primitives::traits::{BlakeTwo256};
+	use runtime_primitives::testing::DigestItem;
 
 	// The testing primitives are very useful for avoiding having to work with signatures
 	// or public keys. `u64` is used as the `AccountId` and no `Signature`s are requried.
@@ -353,6 +354,7 @@ mod tests {
 		type AccountId = u64;
 		type Header = Header;
 		type Event = ();
+		type Log = DigestItem;
 	}
 	impl balances::Trait for Test {
 		type Balance = u64;
@@ -368,7 +370,7 @@ mod tests {
 
 	// This function basically just builds a genesis storage key/value store according to
 	// our desired mockup.
-	fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
+	fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher, RlpCodec> {
 		let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap();
 		// We use default for brevity, but you can configure as desired if needed.
 		t.extend(balances::GenesisConfig::<Test>::default().build_storage().unwrap());