Print out tokens as they come

src/main.rs

@@ -8,5 +8,7 @@ fn main() {
     lexer::hello(&s);
 
     let lexer = lexer::Lexer::new(String::from("((abc))"));
-    for t in lexer { }
+    for t in lexer {
+        println!("token = {}", t);
+    }
 }