Use fully qualified path in macro

As we do for the rest of the macros use the fully qualified path to
`fmt` so users of the macro do not have to import it.

Author: tcharding

src/internal_macros.rs

@@ -84,7 +84,7 @@ macro_rules! impl_array_newtype {
             pub fn into_bytes(self) -> [$ty; $len] { self.0 }
         }
 
-        impl<'a> ::core::convert::From<&'a [$ty]> for $thing {
+        impl<'a> core::convert::From<&'a [$ty]> for $thing {
             fn from(data: &'a [$ty]) -> $thing {
                 assert_eq!(data.len(), $len);
                 let mut ret = [0; $len];
@@ -109,7 +109,7 @@ macro_rules! impl_array_newtype {
 
 macro_rules! display_from_debug {
     ($thing:ident) => {
-        impl ::core::fmt::Display for $thing {
+        impl core::fmt::Display for $thing {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> Result<(), ::core::fmt::Error> {
                 ::core::fmt::Debug::fmt(self, f)
             }
@@ -365,13 +365,13 @@ macro_rules! impl_bytes_newtype {
 
         impl ::core::fmt::Display for $t {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                fmt::LowerHex::fmt(self, f)
+                ::core::fmt::LowerHex::fmt(self, f)
             }
         }
 
         impl ::core::fmt::Debug for $t {
             fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                fmt::LowerHex::fmt(self, f)
+                ::core::fmt::LowerHex::fmt(self, f)
             }
         }