Remove zerocopy from public interface

Instead create a crate-local AsBytes wrapper trait. This trait is not
sealed as Primitive was not sealed, so that users can delegate it for
newtypes if needed.

src/buffer.rs

@@ -8,9 +8,8 @@ use color::{ChannelsType, ColorType, FromColor, Luma, LumaA, Rgb, Rgba, Bgr, Bgr
 use flat::{FlatSamples, SampleLayout};
 use dynimage::{save_buffer, save_buffer_with_format};
 use image::{GenericImage, GenericImageView, ImageFormat, ImageResult};
-use traits::Primitive;
+use traits::{AsBytes, Primitive};
 use utils::expand_packed;
-use zerocopy::AsBytes;
 
 
 /// A generalized pixel.
@@ -745,7 +744,7 @@ where
 impl<P, Container> ImageBuffer<P, Container>
 where
     P: Pixel + 'static,
-    P::Subpixel: AsBytes,
+    [P::Subpixel]: AsBytes,
     Container: Deref<Target = [P::Subpixel]>,
 {
     /// Saves the buffer to a file at the path specified.
@@ -770,7 +769,7 @@ where
 impl<P, Container> ImageBuffer<P, Container>
 where
     P: Pixel + 'static,
-    P::Subpixel: AsBytes,
+    [P::Subpixel]: AsBytes,
     Container: Deref<Target = [P::Subpixel]>,
 {
     /// Saves the buffer to a file at the specified path in

src/traits.rs

@@ -5,6 +5,25 @@
 use num_traits::{Bounded, Num, NumCast};
 use std::ops::AddAssign;
 
+/// Types which are safe to treat as an immutable byte slice. This is a wrapper
+/// around the `zerocopy::AsBytes` trait.
+pub trait AsBytes {
+    /// Get the bytes of this value.
+    fn as_bytes(&self) -> &[u8];
+}
+
+impl<T> AsBytes for T where T: zerocopy::AsBytes {
+    fn as_bytes(&self) -> &[u8] {
+        zerocopy::AsBytes::as_bytes(self)
+    }
+}
+
+impl<T> AsBytes for [T] where [T]: zerocopy::AsBytes {
+    fn as_bytes(&self) -> &[u8] {
+        zerocopy::AsBytes::as_bytes(self)
+    }
+}
+
 /// Primitive trait from old stdlib
 pub trait Primitive: Copy + NumCast + Num + PartialOrd<Self> + Clone + Bounded {}