d: add skeleton for the D language

Contributed by Oliver Mangold.
https://lists.gnu.org/archive/html/help-bison/2012-01/msg00000.html

* README-D.txt, d-skel.m4, d.m4, lalr1.d: New.

data/d-skel.m4

@@ -0,0 +1,26 @@
+                                                            -*- Autoconf -*-
+
+# D skeleton dispatching for Bison.
+
+# Copyright (C) 2018 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+b4_glr_if(             [b4_complain([%%glr-parser not supported for D])])
+b4_nondeterministic_if([b4_complain([%%nondeterministic-parser not supported for D])])
+
+m4_define_default([b4_used_skeleton], [b4_pkgdatadir/[lalr1.d]])
+m4_define_default([b4_skeleton], ["b4_basename(b4_used_skeleton)"])
+
+m4_include(b4_used_skeleton)