Remove io::Cursor, and implement Buf/BufMut for slices instead (#261)

tests/test_take.rs

@@ -1,13 +1,12 @@
 extern crate bytes;
 
 use bytes::Buf;
-use std::io::Cursor;
 
 #[test]
 fn long_take() {
     // Tests that get a take with a size greater than the buffer length will not
     // overrun the buffer. Regression test for #138.
-    let buf = Cursor::new(b"hello world").take(100);
+    let buf = b"hello world".take(100);
     assert_eq!(11, buf.remaining());
     assert_eq!(b"hello world", buf.bytes());
 }