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/src/rpc.rs

@@ -29,11 +29,6 @@ use std::{
 use crate::{
     error::BasicError,
     storage::StorageKeyPrefix,
-    subscription::{
-        EventStorageSubscription,
-        FinalizedEventStorageSubscription,
-        SystemEvents,
-    },
     Config,
     Metadata,
 };
@@ -406,35 +401,6 @@ impl<T: Config> Rpc<T> {
         Ok(version)
     }
 
-    /// Subscribe to System Events that are imported into blocks.
-    ///
-    /// *WARNING* these may not be included in the finalized chain, use
-    /// `subscribe_finalized_events` to ensure events are finalized.
-    pub async fn subscribe_events(
-        &self,
-    ) -> Result<EventStorageSubscription<T>, BasicError> {
-        let keys = Some(vec![StorageKey::from(SystemEvents::new())]);
-        let params = rpc_params![keys];
-
-        let subscription = self
-            .client
-            .subscribe("state_subscribeStorage", params, "state_unsubscribeStorage")
-            .await?;
-        Ok(EventStorageSubscription::Imported(subscription))
-    }
-
-    /// Subscribe to finalized events.
-    pub async fn subscribe_finalized_events(
-        &self,
-    ) -> Result<EventStorageSubscription<T>, BasicError> {
-        Ok(EventStorageSubscription::Finalized(
-            FinalizedEventStorageSubscription::new(
-                self.clone(),
-                self.subscribe_finalized_blocks().await?,
-            ),
-        ))
-    }
-
     /// Subscribe to blocks.
     pub async fn subscribe_blocks(&self) -> Result<Subscription<T::Header>, BasicError> {
         let subscription = self