This modifies the modular reduction step to make use of the same fast
reduce mechanism used in the gcs filters.  As can be seen in the
following benchmark results, it more than doubles the performance of the
primary filter operations.

In order to experimentally validate the mapping adheres to the
theoretical results and doesn't have any adverse effects on the false
positive rates, the same validation methodology described in README.md
was conducted again and said README is updated accordingly.  Everything
is well within the margin of error as expected.

Finally, the README is also updated with the new benchmark results and
the required go version is bumped in the go.mod due to the addition of
the math/bits import.

name                     old time/op    new time/op  delta
-----------------------------------------------------------------------------
capacity=1000, fprate=0.1%
--------------------------
BenchmarkAdd             158ns ± 1%      59ns ± 1%   -62.59%  (p=0.008 n=5+5)
BenchmarkContainsTrue    183ns ± 1%      69ns ± 2%   -62.27%  (p=0.008 n=5+5)
BenchmarkContainsFalse   61.3ns ±40%   42.0ns ±26%   -31.41%  (p=0.032 n=5+5)

capacity=1000, fprate=0.01%
---------------------------
BenchmarkAdd              211ns ± 1%     69ns ± 1%   -67.07%  (p=0.008 n=5+5)
BenchmarkContainsTrue     236ns ± 2%     80ns ± 1%   -66.16%  (p=0.008 n=5+5)
BenchmarkContainsFalse   59.6ns ±24%    37.7ns ± 5%  -36.74%  (p=0.008 n=5+5)
BenchmarkReset

capacity=1000, fprate=0.001%
----------------------------
BenchmarkAdd             247ns ± 0%       78ns ± 2%  -68.32%  (p=0.008 n=5+5)
BenchmarkContainsTrue    272ns ± 1%       89ns ± 1%  -67.50%  (p=0.008 n=5+5)
BenchmarkContainsFalse   58.6ns ±26%    37.0ns ± 4%  -36.98%  (p=0.008 n=5+5)

capacity=100000, fprate=0.01%
-----------------------------
BenchmarkAdd              205ns ± 2%      80ns ± 1%  -61.12%  (p=0.008 n=5+5)
BenchmarkContainsTrue     219ns ± 1%      80ns ± 1%  -63.39%  (p=0.008 n=5+5)
BenchmarkContainsFalse   70.3ns ±46%    37.6ns ±10%  -46.61%  (p=0.008 n=5+5)

capacity=100000, fprate=0.0001%
-------------------------------
BenchmarkAdd              275ns ± 2%     110ns ± 1%  -60.10%  (p=0.008 n=5+5)
BenchmarkContainsTrue     287ns ± 1%      98ns ± 1%  -65.98%  (p=0.008 n=5+5)
BenchmarkContainsFalse   56.6ns ±45%    36.3ns ± 6%  -35.93%  (p=0.008 n=5+5)

capacity=100000, fprate=0.00001%
--------------------------------
BenchmarkAdd             413ns ± 3%     205ns ± 2%  -50.41%  (p=0.016 n=5+5)