d: add support for %printer

Currently we display the addresses of the semantic values.  Instead,
print the values.

Add support for YY_USE across languages.

* data/skeletons/c.m4, data/skeletons/d.m4 (b4_use): New.
* data/skeletons/bison.m4 (b4_symbol_actions): Use b4_use to be
portable to D.

Add support for %printer, and use it.

* data/skeletons/d.m4: Instead of duplicating what's already in
c-like.m4, include it.
(b4_symbol_action): New.
Differs from the one in bison.m4 in that it uses yyval/yyloc instead
of *yyvaluep and *yylocationp.

* data/skeletons/lalr1.d (yy_symbol_print): Avoid calls to formatting,
just call write directly.
Use the %printer.
* examples/d/calc/calc.y: Specify a printer.
Enable traces when $YYDEBUG is set.
* tests/calc.at: Fix the use of %printer with D.

examples/d/calc/calc.y

@@ -21,6 +21,7 @@
 
 %define api.parser.class {Calc}
 %define parse.error verbose
+%define parse.trace
 
 %locations
 
@@ -38,6 +39,7 @@
        EOL    "end of line"
 %token <ival> NUM "number"
 %type  <ival> exp
+%printer { yyo.write($$); } <ival>
 
 %left "-" "+"
 %left "*" "/"
@@ -168,6 +170,9 @@ int main()
 {
   auto l = calcLexer(stdin);
   auto p = new Calc(l);
+  import core.stdc.stdlib : getenv;
+  if (getenv("YYDEBUG"))
+    p.setDebugLevel(1);
   p.parse();
   return l.exit_status;
 }