Automatically generate drop for #[metatype]

crates/luaffi_impl/src/cdef.rs

@@ -1,9 +1,15 @@
 use crate::utils::{ffi_crate, syn_assert, syn_error};
+use darling::FromMeta;
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
 use syn::{spanned::*, *};
 
-pub fn transform(mut item: Item) -> Result<TokenStream> {
+#[derive(Debug, FromMeta)]
+pub struct Args {
+    module: Option<String>,
+}
+
+pub fn transform(args: Args, mut item: Item) -> Result<TokenStream> {
     let (name, impl_type, impl_cdef) = match item {
         Item::Struct(ref mut str) => (
             str.ident.clone(),