Performance:
                  Rate $jac->sim sim only jaccard_string jaccard_bits
$jac->sim      63480/s        --     -21%           -62%         -80%
sim only       79868/s       26%       --           -53%         -75%
jaccard_hash  168300/s      165%     111%             --         -47%
jaccard_bits  318317/s      401%     299%            89%           --