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

codegen/src/api/calls.rs

@@ -90,7 +90,7 @@ pub fn generate_calls(
                 pub fn #fn_name(
                     &self,
                     #( #call_fn_args, )*
-                ) -> ::subxt::SubmittableExtrinsic<'a, T, X, A, #call_struct_name, DispatchError> {
+                ) -> ::subxt::SubmittableExtrinsic<'a, T, X, A, #call_struct_name, DispatchError, root_mod::Event> {
                     let call = #call_struct_name { #( #call_args, )* };
                     ::subxt::SubmittableExtrinsic::new(self.client, call)
                 }
@@ -101,6 +101,7 @@ pub fn generate_calls(
 
     quote! {
         pub mod calls {
+            use super::root_mod;
             use super::#types_mod_ident;
 
             type DispatchError = #types_mod_ident::sp_runtime::DispatchError;