Add #![no_std] (#8)

I would like to use this crate in a #![no_std] program

It doesn't depend on the standard library, so it appears this can safely be
added.

src/lib.rs

@@ -26,6 +26,11 @@
 //! # }
 //! ```
 #![deny(warnings)]
+#![no_std]
+
+#[cfg(test)]
+#[macro_use]
+extern crate std;
 
 /// You can use `array_ref` to generate an array reference to a subset
 /// of a sliceable bit of data (which could be an array, or a slice,
@@ -227,6 +232,8 @@ mod test {
 
 extern crate quickcheck;
 
+use std::vec::Vec;
+
 // use super::*;
 
 #[test]