Added async example which makes multiple requests (#351)

examples/async_multiple_requests.rs

@@ -0,0 +1,55 @@
+#![deny(warnings)]
+
+extern crate futures;
+extern crate reqwest;
+extern crate tokio;
+extern crate serde;
+#[macro_use] extern crate serde_derive;
+extern crate serde_json;
+
+use futures::Future;
+use reqwest::async::{Client, Response};
+
+#[derive(Deserialize, Debug)]
+struct Slideshow {
+    title: String,
+    author: String,
+}
+
+#[derive(Deserialize, Debug)]
+struct SlideshowContainer {
+    slideshow: Slideshow,
+}
+
+fn fetch() -> impl Future<Item=(), Error=()> {
+    let client = Client::new();
+
+    let json = |mut res : Response | {
+        res.json::<SlideshowContainer>()
+    };
+
+    let request1 =
+        client
+            .get("https://httpbin.org/json")
+            .send()
+            .and_then(json);
+
+    let request2 =
+        client
+            .get("https://httpbin.org/json")
+            .send()
+            .and_then(json);
+
+    request1.join(request2)
+        .map(|(res1, res2)|{
+            println!("{:?}", res1);
+            println!("{:?}", res2);
+        })
+        .map_err(|err| {
+            println!("stdout error: {}", err);
+        })
+}
+
+fn main() {
+    tokio::run(fetch());
+}