hashes: Hide macros from docs

These three macros are solely provided to reduce code duplication, they
are only part of the public API because they are used by the "real"
public macro `hash_newtype`.

hashes/src/macros.rs

@@ -3,6 +3,7 @@
 //! Public macros.
 
 /// Adds hexadecimal formatting implementation of a trait `$imp` to a given type `$ty`.
+#[doc(hidden)]
 #[macro_export]
 macro_rules! hex_fmt_impl(
     ($reverse:expr, $len:expr, $ty:ident) => (
@@ -48,6 +49,7 @@ macro_rules! hex_fmt_impl(
 );
 
 /// Adds slicing traits implementations to a given type `$ty`
+#[doc(hidden)]
 #[macro_export]
 macro_rules! borrow_slice_impl(
     ($ty:ident) => (
@@ -439,6 +441,7 @@ pub mod serde_details {
 
 /// Implements `Serialize` and `Deserialize` for a type `$t` which
 /// represents a newtype over a byte-slice over length `$len`.
+#[doc(hidden)]
 #[macro_export]
 #[cfg(feature = "serde")]
 macro_rules! serde_impl(