stddoclet: Add stopindex HTML tags around unimportant text to improve API search

We could improve full text search of API docs if we could prevent search engines
from indexing unimportant text that users would be highly unlikely to be
searching for. Such text includes navigation bars and redundant text such as
the navigation lists of packages and classes that appear in the left-hand
frame.

Inktomi supports the stopping and starting of indexing by way of the following
tags:

  Text to index
<!--stopindex-->
  Text to not index
<!--startindex-->
  Text to index

Source:
http://support.inktomi.com/kb/020701-009.html