Merge #262

262: Move AtomicCell into crossbeam-utils r=jeehoonkang a=stjepang

At this point, I feel pretty confident about the current state of `AtomicCell` in the sense that we probably won't make any breaking changes to its public API in the future.

It's also a reasonably small utility without dependencies that deserves living in `crossbeam-utils`. The Rust compiler would like to use it in place of its `LockCell`, and already has `crossbeam-utils` whitelisted. See [this PR](rust-lang/rust#56614 (comment)).

Let's move `AtomicCell` into `crossbeam-utils` so that people can use it without depending on whole `crossbeam`.

Co-authored-by: Stjepan Glavina <stjepang@gmail.com>

Author: bors[bot]

src/atomic_cell.rs renamed to crossbeam-utils/src/atomic/atomic_cell.rs

@@ -1,5 +1,7 @@
 //! Additional utilities for atomics.
 
+mod atomic_cell;
 mod consume;
 
+pub use self::atomic_cell::AtomicCell;
 pub use self::consume::AtomicConsume;

crossbeam-utils/src/atomic/mod.rs

@@ -59,14 +59,13 @@ mod _epoch {
 pub use _epoch::crossbeam_epoch as epoch;
 
 mod arc_cell;
-mod atomic_cell;
 
 extern crate crossbeam_utils;
 
 /// Additional utilities for atomics.
 pub mod atomic {
     pub use arc_cell::ArcCell;
-    pub use atomic_cell::AtomicCell;
+    pub use crossbeam_utils::atomic::AtomicCell;
     pub use crossbeam_utils::atomic::AtomicConsume;
 }