Remove extern crate statements

https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-clarity.html

src/queue.rs

@@ -1,6 +1,7 @@
 use std::cmp::Ordering;
 use std::sync::{Arc, RwLock};
 
+use log::{debug, error, info};
 #[cfg(feature = "notify")]
 use notify_rust::Notification;