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/events/mod.rs

@@ -0,0 +1,40 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is part of subxt.
+//
+// subxt is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// subxt is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+//! For working with events.
+
+mod decoding;
+mod event_subscription;
+mod events_type;
+mod filter_events;
+
+pub use decoding::EventsDecodingError;
+pub use event_subscription::{
+    subscribe,
+    subscribe_finalized,
+    EventSubscription,
+};
+pub use events_type::{
+    at,
+    EventDetails,
+    Events,
+    RawEventDetails,
+};
+pub use filter_events::{
+    EventFilter,
+    FilterEvents,
+    FilteredEventDetails,
+};