build: warn lints instead of deny

As @roypat pointed out and discussed in [1], using `#![deny(warnings)]`
to enforce clean code could be harmful. Thus changing `deny` lints to
`warn`.

[1] https://www.reddit.com/r/rust/comments/f5xpib/psa_denywarnings_is_actively_harmful/

Signed-off-by: Ruoqing He <[email protected]>

Author: RuoqingHe

src/lib.rs

@@ -15,9 +15,9 @@
 //! without knowing the implementation details of the VM memory provider. Thus hypervisor
 //! components, such as boot loader, virtual device drivers, virtio backend drivers and vhost
 //! drivers etc, could be shared and reused by multiple hypervisors.
-#![deny(clippy::doc_markdown)]
-#![deny(missing_docs)]
-#![deny(missing_debug_implementations)]
+#![warn(clippy::doc_markdown)]
+#![warn(missing_docs)]
+#![warn(missing_debug_implementations)]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 
 // We only support 64bit. Fail build when attempting to build other targets