Change Bytes::make_mut to impl From<Bytes> for BytesMut (closes #709) (#710)

<Arc<T>>::make_mut returns a &mut T, such an API is doable for Bytes too
and thus we should reserve Bytes::make_mut for that.

Furthermore, it would be helpful to use From<Bytes> as a trait bound
in some cases with other traits such as Hyper's body trait, where Hyper
gives you Bytes values.

Finally, making it impl From<Bytes> for BytesMut means the API is more
easily discoverable as it appears on both Bytes and BytesMut.

tests/test_bytes.rs

@@ -1174,29 +1174,29 @@ fn shared_is_unique() {
 }
 
 #[test]
-fn test_bytes_make_mut_static() {
+fn test_bytesmut_from_bytes_static() {
     let bs = b"1b23exfcz3r";
 
     // Test STATIC_VTABLE.to_mut
-    let bytes_mut = Bytes::from_static(bs).make_mut();
+    let bytes_mut = BytesMut::from(Bytes::from_static(bs));
     assert_eq!(bytes_mut, bs[..]);
 }
 
 #[test]
-fn test_bytes_make_mut_bytes_mut_vec() {
+fn test_bytesmut_from_bytes_bytes_mut_vec() {
     let bs = b"1b23exfcz3r";
     let bs_long = b"1b23exfcz3r1b23exfcz3r";
 
     // Test case where kind == KIND_VEC
     let mut bytes_mut: BytesMut = bs[..].into();
-    bytes_mut = bytes_mut.freeze().make_mut();
+    bytes_mut = BytesMut::from(bytes_mut.freeze());
     assert_eq!(bytes_mut, bs[..]);
     bytes_mut.extend_from_slice(&bs[..]);
     assert_eq!(bytes_mut, bs_long[..]);
 }
 
 #[test]
-fn test_bytes_make_mut_bytes_mut_shared() {
+fn test_bytesmut_from_bytes_bytes_mut_shared() {
     let bs = b"1b23exfcz3r";
 
     // Set kind to KIND_ARC so that after freeze, Bytes will use bytes_mut.SHARED_VTABLE
@@ -1207,17 +1207,17 @@ fn test_bytes_make_mut_bytes_mut_shared() {
     let b2 = b1.clone();
 
     // shared.is_unique() = False
-    let mut b1m = b1.make_mut();
+    let mut b1m = BytesMut::from(b1);
     assert_eq!(b1m, bs[..]);
     b1m[0] = b'9';
 
     // shared.is_unique() = True
-    let b2m = b2.make_mut();
+    let b2m = BytesMut::from(b2);
     assert_eq!(b2m, bs[..]);
 }
 
 #[test]
-fn test_bytes_make_mut_bytes_mut_offset() {
+fn test_bytesmut_from_bytes_bytes_mut_offset() {
     let bs = b"1b23exfcz3r";
 
     // Test bytes_mut.SHARED_VTABLE.to_mut impl where offset != 0
@@ -1227,58 +1227,58 @@ fn test_bytes_make_mut_bytes_mut_offset() {
     let b1 = bytes_mut1.freeze();
     let b2 = bytes_mut2.freeze();
 
-    let b1m = b1.make_mut();
-    let b2m = b2.make_mut();
+    let b1m = BytesMut::from(b1);
+    let b2m = BytesMut::from(b2);
 
     assert_eq!(b2m, bs[9..]);
     assert_eq!(b1m, bs[..9]);
 }
 
 #[test]
-fn test_bytes_make_mut_promotable_even_vec() {
+fn test_bytesmut_from_bytes_promotable_even_vec() {
     let vec = vec![33u8; 1024];
 
     // Test case where kind == KIND_VEC
     let b1 = Bytes::from(vec.clone());
-    let b1m = b1.make_mut();
+    let b1m = BytesMut::from(b1);
     assert_eq!(b1m, vec);
 }
 
 #[test]
-fn test_bytes_make_mut_promotable_even_arc_1() {
+fn test_bytesmut_from_bytes_promotable_even_arc_1() {
     let vec = vec![33u8; 1024];
 
     // Test case where kind == KIND_ARC, ref_cnt == 1
     let b1 = Bytes::from(vec.clone());
     drop(b1.clone());
-    let b1m = b1.make_mut();
+    let b1m = BytesMut::from(b1);
     assert_eq!(b1m, vec);
 }
 
 #[test]
-fn test_bytes_make_mut_promotable_even_arc_2() {
+fn test_bytesmut_from_bytes_promotable_even_arc_2() {
     let vec = vec![33u8; 1024];
 
     // Test case where kind == KIND_ARC, ref_cnt == 2
     let b1 = Bytes::from(vec.clone());
     let b2 = b1.clone();
-    let b1m = b1.make_mut();
+    let b1m = BytesMut::from(b1);
     assert_eq!(b1m, vec);
 
     // Test case where vtable = SHARED_VTABLE, kind == KIND_ARC, ref_cnt == 1
-    let b2m = b2.make_mut();
+    let b2m = BytesMut::from(b2);
     assert_eq!(b2m, vec);
 }
 
 #[test]
-fn test_bytes_make_mut_promotable_even_arc_offset() {
+fn test_bytesmut_from_bytes_promotable_even_arc_offset() {
     let vec = vec![33u8; 1024];
 
     // Test case where offset != 0
     let mut b1 = Bytes::from(vec.clone());
     let b2 = b1.split_off(20);
-    let b1m = b1.make_mut();
-    let b2m = b2.make_mut();
+    let b1m = BytesMut::from(b1);
+    let b2m = BytesMut::from(b2);
 
     assert_eq!(b2m, vec[20..]);
     assert_eq!(b1m, vec[..20]);