Add support for the "Aesop Meta Tag".  Not widely used, but not a bad idea,
either.
diff --git a/Doc/tools/mkmodindex b/Doc/tools/mkmodindex
index 23a200e..58ba05e 100755
--- a/Doc/tools/mkmodindex
+++ b/Doc/tools/mkmodindex
@@ -34,6 +34,8 @@
 
 
 class IndexOptions(support.Options):
+    aesop_type = "links"
+
     def __init__(self):
         support.Options.__init__(self)
         self.add_args("l", ["letters"])