Filter one or multiple events by type from an EventSubscription (#461)

* Split events.rs into multiple files and start work on FilterEvents

* First pass filtering event(s)

* Tweak event examples to show filter_events

* cargo clippy + fmt

* consistify and tidy

* cargo fmt

* Tweak a couple of comments

* Expose phase and block_hash of filtered events, too

* cargo fmt

* expose FilteredEventDetails

* Add docs

* cargo clippy

* remove FilterEvents knowledge of EventSubscription so it's easier to unit test

* unit test filter_events

* tweak an integration test to use filter_events

* cargo fmt

* cargo clippy

* Tweak a comment

Co-authored-by: David <dvdplm@gmail.com>

Co-authored-by: David <dvdplm@gmail.com>

subxt/src/transaction.rs

@@ -514,9 +514,9 @@ impl<'client, T: Config, Evs: Decode> TransactionEvents<'client, T, Evs> {
     /// Iterate through the transaction events using metadata to dynamically decode and skip
     /// them, and return the first event found which decodes to the provided `Ev` type.
     ///
-    /// This works in the same way that [`events::Events::find_first_event()`] does, with the
+    /// This works in the same way that [`events::Events::find_first()`] does, with the
     /// exception that it ignores events not related to the submitted extrinsic.
-    pub fn find_first_event<Ev: crate::Event>(&self) -> Result<Option<Ev>, BasicError> {
+    pub fn find_first<Ev: crate::Event>(&self) -> Result<Option<Ev>, BasicError> {
         self.find::<Ev>().next().transpose()
     }