just deprecate the cstr! macro without removing it

Fixes #36

src/modules.rs

@@ -17,6 +17,18 @@ bitflags! {
     }
 }
 
+/// Create a NUL-terminated C string from a string literal
+#[macro_export]
+#[deprecated(note = "use a C-string literal instead")]
+macro_rules! cstr {
+    () => {
+        unsafe { core::ffi::CStr::from_bytes_with_nul_unchecked(b"\0") }
+    };
+    ($s:expr) => {
+        unsafe { core::ffi::CStr::from_bytes_with_nul_unchecked(concat!($s, "\0").as_bytes()) }
+    };
+}
+
 /// An internal module that the kernel requests from the bootloader. Only
 /// available with request revision 1 and greater.
 #[repr(C)]