Split the visit and visit_mut codegen
diff --git a/codegen/src/main.rs b/codegen/src/main.rs
index a83cbfc..8fd5cf9 100644
--- a/codegen/src/main.rs
+++ b/codegen/src/main.rs
@@ -14,14 +14,16 @@
 
 mod file;
 mod fold;
-mod gen;
 mod json;
 mod parse;
 mod version;
+mod visit;
+mod visit_mut;
 
 fn main() {
     let defs = parse::parse();
     json::generate(&defs);
-    gen::generate(&defs);
     fold::generate(&defs);
+    visit::generate(&defs);
+    visit_mut::generate(&defs);
 }