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/balance_transfer.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.
 
-//! To run this example, a local polkadot node should be running. Example verified against polkadot 0.9.13-82616422d0-aarch64-macos.
+//! To run this example, a local polkadot node should be running. Example verified against polkadot 0.9.18-f6d6ab005d-aarch64-macos.
 //!
 //! E.g.
 //! ```bash
@@ -26,8 +26,8 @@ use sp_keyring::AccountKeyring;
 use subxt::{
     ClientBuilder,
     DefaultConfig,
-    DefaultExtra,
     PairSigner,
+    PolkadotExtrinsicParams,
 };
 
 #[subxt::subxt(runtime_metadata_path = "examples/polkadot_metadata.scale")]
@@ -43,12 +43,12 @@ 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 hash = api
         .tx()
         .balances()
-        .transfer(dest, 10_000)
-        .sign_and_submit(&signer)
+        .transfer(dest, 123_456_789_012_345)
+        .sign_and_submit_default(&signer)
         .await?;
 
     println!("Balance transfer extrinsic submitted: {}", hash);