Fix to allowing using on older nightly

src/lib.rs

 #![recursion_limit = "512"]
-#![feature(extern_crate_item_prelude)]
+#![feature(option_replace)]
 // While under active devel, these warnings are kind of annoying.
 #![allow(dead_code)]
 
@@ -241,6 +241,14 @@ use crate::errors::*;
 #[macro_use]
 mod errors;
 
+#[macro_use]
+extern crate quote;
+extern crate syn;
+
+extern crate glib;
+extern crate glib_sys;
+extern crate gobject_sys;
+
 mod ast;
 mod checking;
 mod gen;

src/parser/mod.rs

-use proc_macro;
+extern crate proc_macro;
+
 use proc_macro2::TokenStream;
 use syn::parse::{Parse, ParseStream, Result};
 use syn::{self, braced, parenthesized, Token};