fix: Use core instead of std where it is possible

Author: jhg

src/error.rs

@@ -1,6 +1,6 @@
 //! Opaque pointers errors.
 
-use std::str::Utf8Error;
+use core::str::Utf8Error;
 
 /// Errors that can be detected by the functions of this crate.
 ///
@@ -16,8 +16,8 @@ pub enum PointerError {
     Utf8Error(Utf8Error),
 }
 
-impl std::fmt::Display for PointerError {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+impl core::fmt::Display for PointerError {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         match *self {
             Self::Null => {
                 write!(f, "dereference a null pointer will produce a crash")

src/lib.rs

@@ -95,7 +95,7 @@ pub fn raw<T>(data: T) -> *mut T {
 #[cfg(any(feature = "alloc", feature = "std"))]
 #[inline]
 pub unsafe fn free<T>(pointer: *mut T) {
-    std::mem::drop(own_back(pointer));
+    core::mem::drop(own_back(pointer));
 }
 
 /// Opposite of [`raw<T>()`], to use Rust's ownership as usually.