Retire README.rst, use pandoc to generate README.md.

The rst source has apparently become too large for gitlab web sites
to be able to render it. So we just go with markdown, in the hopes
that gitlab can better cope with it.

It's not an error if you don't have pandoc installed, but then
README will not be kept up to date with the docs in vcc.

Makefile.am

@@ -5,13 +5,19 @@ SUBDIRS = src
 DISTCHECK_CONFIGURE_FLAGS = \
 	VMOD_DIR='$${libdir}/varnish/vmods'
 
-EXTRA_DIST = README.rst
+EXTRA_DIST = README.md
 
-dist_doc_DATA = README.rst LICENSE COPYING
+dist_doc_DATA = README.md LICENSE COPYING
 
-README.rst: src/vmod_re2.vcc
+README.md: src/vmod_re2.vcc
+if HAVE_PANDOC
 	$(MAKE) -C src vmod_re2.man.rst
-	cp src/vmod_re2.man.rst README.rst
+	$(AM_V_GEN) $(PANDOC) -f rst -t gfm src/vmod_re2.man.rst > README.md
+else
+	@echo "========================================================="
+	@echo "You need pandoc installed to generate README.md, skipping"
+	@echo "========================================================="
+endif
 
 coverage:
 	$(MAKE) $(AM_MAKEFLAGS) -C src coverage

configure.ac

@@ -44,6 +44,14 @@ AC_ARG_WITH([genhtml],
 	AC_CHECK_PROGS(GENHTML, [genhtml], []))
 AM_CONDITIONAL(HAVE_GENHTML, [test -n "$GENHTML"])
 
+AC_ARG_WITH([pandoc],
+	AS_HELP_STRING(
+		[--with-pandoc=PATH],
+		[Location of pandoc to generate README.md (auto)]),
+	[PANDOC="$withval"],
+	AC_CHECK_PROGS(PANDOC, [pandoc], []))
+AM_CONDITIONAL(HAVE_PANDOC, [test -n "$PANDOC"])
+
 m4_ifndef([VARNISH_PREREQ], AC_MSG_ERROR([Need varnish.m4 -- see INSTALL.rst]))
 
 PKG_CHECK_MODULES([RE2], [re2])