merge hex & debug into fmt (#357)

src/fmt/hex.rs

@@ -0,0 +1,37 @@
+use core::fmt::{Formatter, LowerHex, Result, UpperHex};
+
+use crate::{Bytes, BytesMut};
+use super::BytesRef;
+
+impl LowerHex for BytesRef<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        for &b in self.0 {
+            write!(f, "{:02x}", b)?;
+        }
+        Ok(())
+    }
+}
+
+impl UpperHex for BytesRef<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        for &b in self.0 {
+            write!(f, "{:02X}", b)?;
+        }
+        Ok(())
+    }
+}
+
+macro_rules! hex_impl {
+    ($tr:ident, $ty:ty) => {
+        impl $tr for $ty {
+            fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                $tr::fmt(&BytesRef(self.as_ref()), f)
+            }
+        }
+    };
+}
+
+hex_impl!(LowerHex, Bytes);
+hex_impl!(LowerHex, BytesMut);
+hex_impl!(UpperHex, Bytes);
+hex_impl!(UpperHex, BytesMut);