New Event Subscription API (#442)

* Add reworked event types

* first pass implementing event subscriptions

* make clear that some methods are private

* comment tidy

* use Events in transaction stuff

* align transaction and event APIs

* remove __private_ prefixes; they are ugly

* fix examples and remove old events and subscription code

* better comments on hidden event functions

* re-add find_first_event; it's used a bunch in tests and examples

* cargo check --all-targets now passes

* Fix up existing event tests

* cargo fmt

* change todo to note

* clippy and doc niggles

* revert to find_first_event

* Add specific subscription related tests

* cargo fmt

* Update tests and add/fix examples

* cargo fmt

* add a little to subscribe_all_events example

* cargo fmt

* move an example comment

* easy access to root mod for more clarity

* add a couple of tests to ensure that events properly decoded until naff bytes

* Simplify EventSubscription Stream impl a little

* Address some PR feedback

subxt/tests/integration/frame/contracts.rs

@@ -18,6 +18,7 @@ use sp_keyring::AccountKeyring;
 
 use crate::{
     node_runtime::{
+        self,
         contracts::{
             calls::TransactionApi,
             events,
@@ -150,8 +151,10 @@ impl ContractsTestContext {
         &self,
         contract: AccountId,
         input_data: Vec<u8>,
-    ) -> Result<TransactionProgress<'_, DefaultConfig, DispatchError>, Error<DispatchError>>
-    {
+    ) -> Result<
+        TransactionProgress<'_, DefaultConfig, DispatchError, node_runtime::Event>,
+        Error<DispatchError>,
+    > {
         log::info!("call: {:?}", contract);
         let result = self
             .contracts_tx()