Custom weightings in Model index no longer work as documented in TS3

UPDATE: The functionality to add custom weightings to your index is no longer working in TS3.  However, the field weights parameter still works on the search function listed above.  See: https://groups.google.com/forum/#!msg/thinking-sphinx/0cJPILuS5zs/cGvhe2-sZi0J

Contributed by @eschatonsys