Move "extra" methods to extension traits (#306)

tests/test_reader.rs

@@ -2,13 +2,13 @@
 
 use std::io::{BufRead, Read};
 
-use bytes::Buf;
+use bytes::buf::{BufExt};
 
 #[test]
 fn read() {
     let buf1 = &b"hello "[..];
     let buf2 = &b"world"[..];
-    let buf = Buf::chain(buf1, buf2); // Disambiguate with Read::chain
+    let buf = BufExt::chain(buf1, buf2); // Disambiguate with Read::chain
     let mut buffer = Vec::new();
     buf.reader().read_to_end(&mut buffer).unwrap();
     assert_eq!(b"hello world", &buffer[..]);
@@ -18,7 +18,7 @@ fn read() {
 fn buf_read() {
     let buf1 = &b"hell"[..];
     let buf2 = &b"o\nworld"[..];
-    let mut reader = Buf::chain(buf1, buf2).reader();
+    let mut reader = BufExt::chain(buf1, buf2).reader();
     let mut line = String::new();
     reader.read_line(&mut line).unwrap();
     assert_eq!("hello\n", &line);