make regular expression groups non-capturing
make regular expression groups non-capturing

`benchstat` vs. master@588e8594267cca0d170ceda20342f7a883b80153:

    name             old time/op    new time/op    delta
    StrictEmpty-4      15.0ns ± 1%    15.1ns ± 1%   +0.99%  (p=0.000 n=7+9)
    StrictSingle-4     41.2µs ± 4%    37.7µs ± 3%   -8.56%  (p=0.000
    n=10+10)
    StrictMany-4        125µs ± 1%     116µs ± 1%   -7.51%  (p=0.000
    n=10+10)
    RelaxedEmpty-4     15.2µs ± 3%    13.2µs ± 1%  -13.61%  (p=0.000
    n=10+10)
    RelaxedSingle-4    95.3µs ± 5%    80.0µs ± 1%  -15.98%  (p=0.000 n=10+8)
    RelaxedMany-4       247µs ± 1%     217µs ± 4%  -12.13%  (p=0.000 n=9+10)

    name             old alloc/op   new alloc/op   delta
    StrictEmpty-4       0.00B          0.00B          ~     (all equal)
    StrictSingle-4       364B ± 4%      276B ± 1%  -24.03%  (p=0.000 n=9+7)
    StrictMany-4         792B ± 6%      515B ± 0%  -35.04%  (p=0.000 n=10+7)
    RelaxedEmpty-4      73.8B ± 2%      7.0B ± 0%  -90.51%  (p=0.000 n=10+7)
    RelaxedSingle-4    2.43kB ± 4%    1.50kB ± 4%  -38.35%  (p=0.000 n=9+10)
    RelaxedMany-4      5.02kB ± 3%    2.82kB ± 7%  -43.87%  (p=0.000
    n=10+10)

    name             old allocs/op  new allocs/op  delta
    StrictEmpty-4        0.00           0.00          ~     (all equal)
    StrictSingle-4       2.00 ± 0%      2.00 ± 0%     ~     (all equal)
    StrictMany-4         4.00 ± 0%      4.00 ± 0%     ~     (all equal)
    RelaxedEmpty-4       0.00           0.00          ~     (all equal)
    RelaxedSingle-4      4.00 ± 0%      3.00 ± 0%  -25.00%  (p=0.000
    n=10+10)
    RelaxedMany-4        8.00 ± 0%      5.00 ± 0%  -37.50%  (p=0.002 n=8+10)

mvdan/xurls