signal: Add an example for waiting on two signals

Relies on `Stream::select` to merge streams.

Closes alexcrichton/tokio-signal#16

examples/multiple.rs

@@ -0,0 +1,38 @@
+//! A small example of how to listen for two signals at the same time
+
+extern crate futures;
+extern crate tokio_core;
+extern crate tokio_signal;
+
+use futures::{Stream, Future};
+use tokio_core::reactor::Core;
+use tokio_signal::unix::{Signal, SIGINT, SIGTERM};
+
+fn main() {
+    let mut core = Core::new().unwrap();
+    let handle = core.handle();
+
+    // Create a stream for each of the signals we'd like to handle.
+    let sigint = Signal::new(SIGINT, &handle).flatten_stream();
+    let sigterm = Signal::new(SIGTERM, &handle).flatten_stream();
+
+    // Use the `select` combinator to merge these two streams into one
+    let stream = sigint.select(sigterm);
+
+    // Wait for a signal to arrive
+    println!("Waiting for SIGINT or SIGTERM");
+    println!("  TIP: use `pkill -sigint multiple` from a second terminal \
+                to send a SIGINT to all processes named 'multiple' \
+                (i.e. this binary)");
+    let (item, _rest) = core.run(stream.into_future()).ok().unwrap();
+
+    // Figure out which signal we received
+    let item = item.unwrap();
+    if item == SIGINT {
+        println!("received SIGINT");
+    } else {
+        assert_eq!(item, SIGTERM);
+        println!("received SIGTERM");
+    }
+}
+