Switch to side-by-side view

--- a/src/doc/user/Makefile
+++ b/src/doc/user/Makefile
@@ -1,2 +1,5 @@
-usermanual.html: usermanual.sgml
+usermanual.html: usermanual.xml
 	sh xmlmake.sh
+
+clean:
+	rm -f RCL.*.html usermanual.pdf usermanual.html index.html