examples: sort them per language and complete them

Convert some of the READMEs to Markdown, which is now more common, and
nicely displayed in some git hosting services.

Add missing READMEs and Makefiles.  Generate XML, HTML and Dot files.  Be
sure to ship the test files.  Complete CLEANFILES to remove all generated
files.

* examples/calc++: Move into...
* examples/c++: here.
* examples/mfcalc, examples/rpcalc: Move into...
* examples/c: here.

* examples/README.md, examples/c++/calc++/Makefile, examples/c/local.mk,
* examples/c/mfcalc/Makefile, examples/c/rpcalc/Makefile,
* examples/d/README.md, examples/java/README.md:
New files.

* examples/test (medir): Be robust to deeper directory nesting.

examples/c/mfcalc/mfcalc.test

@@ -0,0 +1,27 @@
+#! /bin/sh
+
+# Copyright (C) 2005-2015, 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/>.
+
+cat >input <<EOF
+1+2*3
+EOF
+run 0 7
+
+cat >input <<EOF
+(1+2) * 3
+EOF
+run 0 9
+run -noerr 0 9 -p