doc: Change API crate doc-comment to top of file

Author: jhg

src/lib.rs

@@ -1,3 +1,7 @@
+//! # FFI opaque pointers.
+//! 
+//! FFI to use Rust objects from C as opaque pointer.
+
 #![allow(unsafe_code)]
 #![warn(missing_docs)]
 #![warn(clippy::pedantic)]
@@ -6,10 +10,6 @@
 
 #![no_std]
 
-//! # C FFI opaque pointers.
-//! 
-//! FFI to use Rust objects from C as opaque pointer.
-
 #[cfg(not(feature = "std"))]
 extern crate alloc;
 #[cfg(not(feature = "std"))]