Rename some files

* Use "legacy" instead of "stable" since `futures 0.1` is quicly
  becoming "legacy"
* Rename "atomics" to "legacy_atomics" to leave room for the
  libstd-based futures atomics version.
* Rename "polyfill" to "wait_async_polyfill" to specify what it's
  polyfilling.

crates/futures/src/legacy_atomics.rs

@@ -160,7 +160,7 @@ fn wait_async(ptr: &AtomicI32, val: i32) -> js_sys::Promise {
     // If `Atomics.waitAsync` isn't defined (as it isn't defined anywhere today)
     // then we use our fallback, otherwise we use the native function.
     if Atomics::get_wait_async().is_undefined() {
-        crate::polyfill::wait_async(ptr, val)
+        crate::wait_async_polyfill::wait_async(ptr, val)
     } else {
         let mem = wasm_bindgen::memory().unchecked_into::<js_sys::WebAssembly::Memory>();
         Atomics::wait_async(&mem.buffer(), ptr as *const AtomicI32 as i32 / 4, val)

crates/futures/src/lib.rs

@@ -112,15 +112,15 @@ pub use legacy_js2rust::*;
 cfg_if! {
     if #[cfg(target_feature = "atomics")] {
         /// Contains a thread-safe version of this crate, with Futures 0.1
-        mod atomics;
+        mod legacy_atomics;
 
         /// Polyfill for `Atomics.waitAsync` function
-        mod polyfill;
+        mod wait_async_polyfill;
 
-        pub use atomics::*;
+        pub use legacy_atomics::*;
     } else {
-        mod stable;
+        mod legacy;
-        pub use stable::*;
+        pub use legacy::*;
      }
 }