Made sorted() raise an exception instead of aborting when given no arguments; moved around some things in objfun.c as a consequence
diff --git a/py/builtin.c b/py/builtin.c
index 2d61cd6..53ae93a 100644
--- a/py/builtin.c
+++ b/py/builtin.c
@@ -314,4 +314,4 @@
 
     return self;
 }
-MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj, mp_builtin_sorted);
+MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_sorted_obj, 1, mp_builtin_sorted);