Events sub (#126)

* Make event subscription logic more generic.

* Fix build.

* Add test-node.

* Update deps.

* Address review comments.

test-node/src/cli.rs

@@ -0,0 +1,30 @@
+// Copyright 2019-2020 Parity Technologies (UK) Ltd.
+// This file is part of substrate-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 substrate-subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+use sc_cli::{
+    RunCmd,
+    Subcommand,
+};
+use structopt::StructOpt;
+
+#[derive(Debug, StructOpt)]
+pub struct Cli {
+    #[structopt(subcommand)]
+    pub subcommand: Option<Subcommand>,
+
+    #[structopt(flatten)]
+    pub run: RunCmd,
+}