Prepare release v0.2.1 (3rd attempt)

asynchronix/src/executor/task/tests/general.rs

@@ -1,7 +1,6 @@
-use std::future::Future;
 use std::ops::Deref;
 use std::pin::Pin;
-use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicUsize};
 use std::sync::{Arc, Mutex};
 use std::task::{Context, Poll};
 use std::thread;

asynchronix/src/executor/tests.rs

@@ -1,5 +1,3 @@
-use std::sync::atomic::{AtomicUsize, Ordering};
-
 use futures_channel::{mpsc, oneshot};
 use futures_util::StreamExt;