Switch to side-by-side view

--- a/doc/Makefile
+++ b/doc/Makefile
@@ -4,7 +4,7 @@
 	asciidoc $<
 
 all: upplay.html searching.html upplay-releases.html upplay-mingw.html \
-     install.html
+     install.html songcast.html
 
 clean:
 	rm -f *.html