Remove `no_run` from doc tests
//!
//! # Examples
//!
-//! ```no_run
+//! ```
//! extern crate gumdrop;
//! #[macro_use] extern crate gumdrop_derive;
//!
//! `derive(Options)` can also be used on `enum`s to produce a subcommand
//! option parser.
//!
-//! ```no_run
+//! ```
//! extern crate gumdrop;
//! #[macro_use] extern crate gumdrop_derive;
//!
