doc: add gtk-doc to generate documentation

Current limitation is horrible no support to sections: we have to to
have separate header files or to maintain the libkmod-sections.txt file.
We are doing the latter.
diff --git a/configure.ac b/configure.ac
index 7ba29be..bbb4d1f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -128,8 +128,12 @@
 AC_CONFIG_HEADERS(config.h)
 AC_CONFIG_FILES([
 	Makefile
+	libkmod/docs/Makefile
+	libkmod/docs/version.xml
 ])
 
+GTK_DOC_CHECK([1.14],[--flavour no-tmpl-flat])
+
 AC_OUTPUT
 AC_MSG_RESULT([
 	$PACKAGE $VERSION
@@ -151,4 +155,5 @@
 	logging:		${enable_logging}
 	compression:		xz=${with_xz}  zlib=${with_zlib}
 	debug:			${enable_debug}
+	doc:			${enable_gtk_doc}
 ])