docs: enable warnings in doctests

See https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#showing-warnings-in-doctests

Signed-off-by: Martin Kröning <[email protected]>

Author: mkroening

src/lib.rs

@@ -41,6 +41,9 @@
 #![cfg_attr(feature = "very_unstable", feature(effects))]
 #![warn(missing_docs)]
 #![deny(unsafe_op_in_unsafe_fn)]
+#![doc(test(attr(deny(warnings))))]
+#![doc(test(attr(allow(dead_code))))]
+#![doc(test(attr(allow(unused_variables))))]
 
 pub use volatile_ptr::VolatilePtr;
 pub use volatile_ref::VolatileRef;