update example error handling

- Add error-chain dev dependency
- Add error handling using `?` instead of `unwrap`

examples/response_json.rs

@@ -1,15 +1,24 @@
-// cargo run --example response_json
+//! `cargo run --example response_json`
 extern crate reqwest;
+#[macro_use] extern crate serde_derive;
+#[macro_use] extern crate error_chain;
 
-#[macro_use]
-extern crate serde_derive;
+error_chain! {
+    foreign_links {
+        ReqError(reqwest::Error);
+    }
+}
 
 #[derive(Debug, Deserialize)]
 struct Response {
     origin: String,
 }
 
-fn main() {
-    let mut res = reqwest::get("https://httpbin.org/ip").unwrap();
-    println!("JSON: {:?}", res.json::<Response>());
+fn run() -> Result<()> {
+    let mut res = reqwest::get("https://httpbin.org/ip")?;
+    let json = res.json::<Response>()?;
+    println!("JSON: {:?}", json);
+    Ok(())
 }
+
+quick_main!(run);