Simplified tuple returned by string._formatter_parser to only have
4 elements.  No need for old is_markup element, the same information
is indicated by literal_string being None.

Factored string.Formatter class to make subclasses easier to write.
diff --git a/Objects/stringlib/string_format.h b/Objects/stringlib/string_format.h
index 44c5442..b8ea03f 100644
--- a/Objects/stringlib/string_format.h
+++ b/Objects/stringlib/string_format.h
@@ -979,17 +979,12 @@
         /* if 0, error has already been set, if 1, iterator is empty */
         return NULL;
     else {
-        PyObject *is_markup_bool = NULL;
         PyObject *literal_str = NULL;
         PyObject *field_name_str = NULL;
         PyObject *format_spec_str = NULL;
         PyObject *conversion_str = NULL;
         PyObject *tuple = NULL;
 
-        is_markup_bool = PyBool_FromLong(is_markup);
-        if (!is_markup_bool)
-            return NULL;
-
         if (is_markup) {
             /* field_name, format_spec, and conversion are returned */
             literal_str = Py_None;
@@ -1030,11 +1025,9 @@
             Py_INCREF(format_spec_str);
             Py_INCREF(conversion_str);
         }
-        tuple = PyTuple_Pack(5, is_markup_bool, literal_str,
-                             field_name_str, format_spec_str,
+        tuple = PyTuple_Pack(4, literal_str, field_name_str, format_spec_str,
                              conversion_str);
     error:
-        Py_XDECREF(is_markup_bool);
         Py_XDECREF(literal_str);
         Py_XDECREF(field_name_str);
         Py_XDECREF(format_spec_str);