Make sp_core and sp_runtime dependencies optional, and bump to latest (#760)

* begin porting over traits; remove Config use of Hash

* port over the Header bits that we need

* sp_core_hashing where possible, move Verify to PairSigner, remove unused errors

* tidy up Config things and move related bits into one place

* fix codegen

* copy Era over

* move AccountId, Address, Signer to Signer trait and a pass over fixing examples

* impl MultiAddress, MultiSignature, AccountId32 and add back to Config (for decoding later)

* Copy over StorageKey, StorageData, StorageChangeSet

* subxt core compiling with no sp_core or sp_runtime

* Get examples compiling

* pass over fixing tests

* cargo fmt

* clippy tweaks and update polkadot.rs

* fix codegen docs

* port over special DigestItem encoding/decoding

* clippy and doc fixes

* cargo fmt and example fix

* more cargo fmt-ing...

* substrate-extra to substrate-compat

* cargo.toml comments

* simplify PairSigner trait bounds

* move RPC types to a separate file

* fix docs

* Add some tests for things and other PR feedback

* bump to latest sp deps

* avoid needing substrate-compat feature in a test

subxt/src/events/events_client.rs

@@ -6,13 +6,10 @@ use crate::{
     client::OnlineClientT,
     error::Error,
     events::Events,
+    rpc::types::StorageKey,
     Config,
 };
 use derivative::Derivative;
-use sp_core::{
-    storage::StorageKey,
-    twox_128,
-};
 use std::future::Future;
 
 /// A client for working with events.
@@ -74,8 +71,8 @@ where
 
 // The storage key needed to access events.
 fn system_events_key() -> StorageKey {
-    let mut storage_key = twox_128(b"System").to_vec();
-    storage_key.extend(twox_128(b"Events").to_vec());
+    let mut storage_key = sp_core_hashing::twox_128(b"System").to_vec();
+    storage_key.extend(sp_core_hashing::twox_128(b"Events").to_vec());
     StorageKey(storage_key)
 }