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

examples/examples/balance_transfer_with_params.rs

@@ -12,14 +12,16 @@
 
 use sp_keyring::AccountKeyring;
 use subxt::{
-    tx::{
-        Era,
-        PairSigner,
-        PlainTip,
-        PolkadotExtrinsicParamsBuilder as Params,
+    config::{
+        polkadot::{
+            Era,
+            PlainTip,
+            PolkadotExtrinsicParamsBuilder as Params,
+        },
+        PolkadotConfig,
     },
+    tx::PairSigner,
     OnlineClient,
-    PolkadotConfig,
 };
 
 #[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata.scale")]