implement vectors

src/lisp_object.cpp

@@ -21,6 +21,7 @@ proc Lisp_Object_Type_to_string(Lisp_Object_Type type) -> const char* {
     case(Lisp_Object_Type::CFunction):    return "C-function";
     case(Lisp_Object_Type::Continuation): return "continuation";
     case(Lisp_Object_Type::Pair):         return "pair";
+    case(Lisp_Object_Type::Vector):         return "vector";
     }
     return "unknown";
 }