examples: add a complete example with all the bells and whistles

* examples/c/bistromathic/Makefile,
* examples/c/bistromathic/README.md,
* examples/c/bistromathic/bistromathic.test,
* examples/c/bistromathic/local.mk,
* examples/c/bistromathic/parse.y,
* examples/c/bistromathic/scan.l:
New.

* Makefile.am (AM_YFLAGS_WITH_LINES): Add -Wdangling-alias.
* examples/test: Make failure errors easier to read.

examples/c/bistromathic/README.md

@@ -0,0 +1,32 @@
+# bistromathic - all the bells and whistles
+This example demonstrates the best practices when using Bison.
+- Its interface is pure.
+- It uses a custom syntax error with location tracking, lookahead correction
+  and token internationalization.
+- It enables debug trace support with formatting of semantic values.
+
+It also uses Flex to generate the scanner.
+
+<!---
+Local Variables:
+fill-column: 76
+ispell-dictionary: "american"
+End:
+
+Copyright (C) 2020 Free Software Foundation, Inc.
+
+This file is part of Bison, the GNU Compiler Compiler.
+
+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/>.
+--->