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/test

@@ -89,7 +89,9 @@ run ()
     if test "$out_eff" = "$out_exp"; then
       echo "$me: PASS: $number"
     else
-      echo "$me: FAIL: $number (expected output: $out_exp, effective: $out_eff)"
+      echo "$me: FAIL: $number"
+      echo "$me: expected output:  $out_exp"
+      echo "$me: effective output: $out_eff"
       cat err_eff
       exit=false
     fi