improved REPL a bit

now uses rustyline for input

vm/src/value.rs

@@ -1,17 +1,12 @@
 use std::fmt::Display;
 
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq)]
 pub enum Value {
+    #[default]
     Nil,
     Number(f64),
 }
 
-impl Default for Value {
-    fn default() -> Self {
-        Value::Nil
-    }
-}
-
 impl Display for Value {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {