Generate CStr with bindgen

Per documentation, `generate_cstr` should be enabled for all projects because pretty soon it will become the default. See [docs](https://docs.rs/bindgen/latest/bindgen/struct.Builder.html#method.generate_cstr).

Also update the bindings file.

build.rs

@@ -36,6 +36,7 @@ fn main() {
         .derive_copy(true)
         .derive_debug(true)
         .derive_default(true)
+        .generate_cstr(true)
         .generate()
         .expect("Unable to generate bindings");