feat: recursive builtins

src/bin/repl.rs

@@ -6,7 +6,7 @@ use nixjit::*;
 fn main() -> Result<()> {
     let mut rl = DefaultEditor::new()?;
     loop {
-        let readline = rl.readline(">> ");
+        let readline = rl.readline("nixjit-repl> ");
         match readline {
             Ok(expr) => {
                 if expr.trim().is_empty() {