Add deny(missing_debug_implementations) lint

Prevent future additions of types that do not derive Debug where
possible.

Signed-off-by: Carlos López <[email protected]>

Author: 00xc

src/lib.rs

@@ -6,6 +6,7 @@
 // found in the THIRD-PARTY file.
 #![deny(missing_docs)]
 #![deny(missing_copy_implementations)]
+#![deny(missing_debug_implementations)]
 
 //! A safe wrapper around the kernel's KVM interface.
 //!