Fix some minor documentation problems.
Document policy-based thrust::equal.
Document policy-based extrema functions.
Document policy-based thrust::fill and thrust::fill_n.
Document policy-based thrust::find, thrust::find_if, and thrust::find_if_not.
Document policy-based thrust::gather and thrust::gather_if.
Document policy-based thrust::generate and thrust::generate_n.
Document policy-based thrust::inner_product.
Document policy-based thrust::all_of, thrust::any_of, and thrust::none_of.
Document policy-based thrust::merge and thrust::merge_by_key.
Document policy-based thrust::mismatch.
Document policy-based thrust::partition, thrust::partition_copy,
thrust::stable_partition, thrust::stable_partition_copy,
thrust::partition_point, and thrust::is_partitioned.