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

codegen/src/api/calls.rs

@@ -116,7 +116,7 @@ pub fn generate_calls(
             impl<'a, T, X> TransactionApi<'a, T, X>
             where
                 T: ::subxt::Config,
-                X: ::subxt::SignedExtra<T>,
+                X: ::subxt::extrinsic::ExtrinsicParams<T>,
             {
                 pub fn new(client: &'a ::subxt::Client<T>) -> Self {
                     Self { client, marker: ::core::marker::PhantomData }