Change feature annotations in lib.rs to use doc_auto_cfg.

Signed-off-by: Jackson Brim <jackson.cr.brim@gmail.com>

src/lib.rs

@@ -18,8 +18,7 @@
 #![deny(clippy::doc_markdown)]
 #![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
-#![cfg_attr(docsrs, feature(doc_cfg))]
-#![cfg_attr(docsrs, allow(unused_attributes))]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
 
 // We only support 64bit. Fail build when attempting to build other targets
 #[cfg(not(target_pointer_width = "64"))]
@@ -30,7 +29,6 @@ pub mod address;
 pub use address::{Address, AddressValue};
 
 #[cfg(feature = "backend-atomic")]
-#[cfg_attr(docsrs, doc(cfg(feature = "backend-atomic")))]
 pub mod atomic;
 #[cfg(feature = "backend-atomic")]
 pub use atomic::{GuestMemoryAtomic, GuestMemoryLoadGuard};
@@ -65,7 +63,6 @@ mod mmap_xen;
 mod mmap_windows;
 
 #[cfg(feature = "backend-mmap")]
-#[cfg_attr(docsrs, doc(cfg(feature = "backend-mmap")))]
 pub mod mmap;
 
 #[cfg(feature = "backend-mmap")]