* 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
James Wilson