test: Add a benchmark for parsing unquoted data uris.

Current values: test tests::unquoted_url ... bench:     580,075 ns/iter (+/- 15,881)

Author: emilio

src/lib.rs

@@ -5,6 +5,7 @@
 #![crate_name = "cssparser"]
 #![crate_type = "rlib"]
 
+#![feature(test)]
 #![deny(missing_docs)]
 
 /*!