Make sure README.md is tested.

Fixes #18.

.travis.yml

@@ -32,7 +32,7 @@ install:
 script:
     - cargo test --no-default-features
     - cargo test
-    - if [ "$TRAVIS_RUST_VERSION" = 'nightly' ]; then cargo bench --features=bench; fi
+    - if [ "$TRAVIS_RUST_VERSION" = 'nightly' ]; then cargo test --features bench && cargo bench --features bench; fi
     - cargo test --target i686-$OS
 
 after_success:

README.md

@@ -108,7 +108,7 @@ fn main() {
         .dark_color(svg::Color("#800000"))
         .light_color(svg::Color("#ffff80"))
         .build();
-    println!("{}", string);
+    println!("{}", image);
 }
 ```
 

src/lib.rs

@@ -29,12 +29,15 @@
 //! }
 //! ```
 
-#![cfg_attr(feature = "bench", feature(test))] // Unstable libraries
+#![cfg_attr(feature = "bench", feature(test, external_doc))] // Unstable libraries
 #![cfg_attr(feature = "cargo-clippy", deny(warnings, clippy_pedantic))]
 #![cfg_attr(feature = "cargo-clippy",
             allow(unreadable_literal, missing_docs_in_private_items, shadow_reuse,
                   range_plus_one))]
 
+#![cfg_attr(feature = "bench", doc(include = "../README.md"))]
+// ^ make sure we can test our README.md.
+
 extern crate checked_int_cast;
 #[cfg(feature = "image")]
 extern crate image;