index template will now default to accepting input from stdin if do-index is undefined

tpl/index

@@ -63,7 +63,14 @@ cat <<EOH
 EOH
 
 # generate index and populate statistical vars
-do-index output-heading output-line close-heading
+type do-index &>/dev/null \
+  && do-index output-heading output-line close-heading \
+  || {
+    # no do-index is defined; default to accepting input from stdin
+    yearrange="$( date +%Y )"
+    lastts="$( date +%s )"
+    cat
+  }
 
 cat <<EOF
     <footer>