Simplify creating and signing extrinsics (#490)

* WIP extrinsic api updates

* First pass done; now to get things compiling again

* document and tweak new structs/traits

* cargo check --all-targets now compiles without issue

* Polkadot and Substrate take different extra params; support both

* Fix transaction format (missing byte from AccountId -> Address) and fmt

* Tweak Signer trait

* Tweak comments and such in extrinsic params

* check all examples against newer polkadot, add new one with params, import path tweaks

* clippy fix, and save an allocation when signing

* Remove unnecessary Default clauses

* Tidy up and fix comments. Panic if payload size >4GB

* fix typo

examples/examples/fetch_staking_details.rs

@@ -31,7 +31,7 @@ use subxt::{
     sp_runtime::AccountId32,
     ClientBuilder,
     DefaultConfig,
-    DefaultExtra,
+    PolkadotExtrinsicParams,
 };
 
 #[subxt::subxt(runtime_metadata_path = "examples/polkadot_metadata.scale")]
@@ -44,7 +44,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let api = ClientBuilder::new()
         .build()
         .await?
-        .to_runtime_api::<polkadot::RuntimeApi<DefaultConfig, DefaultExtra<DefaultConfig>>>();
+        .to_runtime_api::<polkadot::RuntimeApi<DefaultConfig, PolkadotExtrinsicParams<DefaultConfig>>>();
 
     let era = api.storage().staking().active_era(None).await?.unwrap();
     println!(