Return filtered results when :filtered_result is present.

@scotthain Sorry if this is a clumsy way to submit code to your branch, here.

It turns out that the result filter was being applied to the search results, but was not actually getting returned with the results.

One thing that needs to be decided is the format of the return from `search` when `:filter_result` is present. The `partial_search` function from the Partial Search cookbook returns an array of hashes with the filtered values. Currently, `search` returns an array with the array of filtered hashes, `start`, and `total`. I suppose @lamont-granquist, @sethvargo, or @jtimberman could weigh in here.

Also, I deleted the copypasta'd tests. Looks like that was from back when there were two different search methods?