support no-std (#6)

src/lib.rs

@@ -1,10 +1,13 @@
 #![doc = include_str!("../README.md")]
 #![deny(unsafe_op_in_unsafe_fn)]
+#![no_std]
+
+extern crate alloc;
 
 mod raw;
 
-use std::fmt;
-use std::ops::Index;
+use core::fmt;
+use core::ops::Index;
 
 /// Creates a [`Vec`] containing the given elements.
 ///

src/raw.rs

@@ -1,8 +1,10 @@
-use std::cell::UnsafeCell;
-use std::mem::{self, MaybeUninit};
-use std::ops::Index;
-use std::sync::atomic::{AtomicBool, AtomicPtr, AtomicU64, AtomicUsize, Ordering};
-use std::{ptr, slice};
+use core::cell::UnsafeCell;
+use core::mem::{self, MaybeUninit};
+use core::ops::Index;
+use core::sync::atomic::{AtomicBool, AtomicPtr, AtomicU64, AtomicUsize, Ordering};
+use core::{ptr, slice};
+
+use alloc::boxed::Box;
 
 const BUCKETS: usize = (usize::BITS as usize) - SKIP_BUCKET;
 const MAX_ENTRIES: usize = usize::MAX - SKIP;