Rename Buf/BufMut, methods to chunk/chunk_mut (#450)

The `bytes()` / `bytes_mut()` name implies the method returns the full
set of bytes represented by `Buf`/`BufMut`. To rectify this, the methods
are renamed to `chunk()` and `chunk_mut()` to reflect the partial nature
of the returned byte slice.

`bytes_vectored()` is renamed `chunks_vectored()`.

Closes #447

src/bytes_mut.rs

@@ -445,7 +445,7 @@ impl BytesMut {
             let additional = new_len - len;
             self.reserve(additional);
             unsafe {
-                let dst = self.bytes_mut().as_mut_ptr();
+                let dst = self.chunk_mut().as_mut_ptr();
                 ptr::write_bytes(dst, value, additional);
                 self.set_len(new_len);
             }
@@ -944,7 +944,7 @@ impl Buf for BytesMut {
     }
 
     #[inline]
-    fn bytes(&self) -> &[u8] {
+    fn chunk(&self) -> &[u8] {
         self.as_slice()
     }
 
@@ -985,7 +985,7 @@ unsafe impl BufMut for BytesMut {
     }
 
     #[inline]
-    fn bytes_mut(&mut self) -> &mut UninitSlice {
+    fn chunk_mut(&mut self) -> &mut UninitSlice {
         if self.capacity() == self.len() {
             self.reserve(64);
         }
@@ -1000,7 +1000,7 @@ unsafe impl BufMut for BytesMut {
         Self: Sized,
     {
         while src.has_remaining() {
-            let s = src.bytes();
+            let s = src.chunk();
             let l = s.len();
             self.extend_from_slice(s);
             src.advance(l);