rename parser_class_name as api.parser.class

The previous name was historical and inconsistent.

* src/muscle-tab.c (define_directive): Use the proper value passing
syntax, based on the muscle kind.
(muscle_percent_variable_update): Use the right value passing syntax.
Migrate from parser_class_name to api.parser.class.

* data/skeletons: Migrate from parser_class_name to api.parser.class.

* doc/bison.texi (%define Summary): Document both parser_class_name
and api.parser.class.
Promote the latter over the former.

examples/d/calc.y

@@ -1,6 +1,6 @@
 %language "D"
 %name-prefix "Calc"
-%define parser_class_name {Calc}
+%define api.parser.class {Calc}
 %define public
 
 %define parse.error verbose