test(readme): test readme code fences

.travis/readme.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python
+
+import re
+
+f = open('README.md', 'r')
+raw = f.read()
+
+for (i, code) in enumerate(re.findall(r'```rust([^`]*)```', raw, re.M)):
+    with open('examples/readme_%s.rs' % i, 'w') as f:
+        f.write('#![deny(warnings)]%s' % code)