Simplified push method; updated first and max slice sizes

[christianrpetrin]

These changes yield some pretty good performance improvements.

benchstat old.txt new.txt
name                    old time/op    new time/op    delta
Microservice/0-4          4.95ns ± 1%    4.73ns ± 2%   -4.29%  (p=0.000 n=10+10)
Microservice/1-4           279ns ± 1%     257ns ± 1%   -7.74%  (p=0.000 n=10+10)
Microservice/10-4         2.02µs ± 0%    1.81µs ± 1%  -10.57%  (p=0.000 n=10+10)
Microservice/100-4        18.4µs ± 0%    16.5µs ± 0%  -10.55%  (p=0.000 n=10+10)
Microservice/1000-4        174µs ± 1%     162µs ± 1%   -7.32%  (p=0.000 n=9+10)
Microservice/10000-4      1.79ms ± 1%    1.69ms ± 1%   -5.34%  (p=0.000 n=10+9)
Microservice/100000-4     19.9ms ± 1%    19.6ms ± 1%   -1.47%  (p=0.000 n=10+10)
Microservice/1000000-4     210ms ± 2%     215ms ± 2%   +2.51%  (p=0.003 n=10+9)

name                    old alloc/op   new alloc/op   delta
Microservice/0-4           0.00B          0.00B          ~     (all equal)
Microservice/1-4            224B ± 0%      272B ± 0%  +21.43%  (p=0.000 n=10+10)
Microservice/10-4         1.49kB ± 0%    1.54kB ± 0%   +3.23%  (p=0.000 n=10+10)
Microservice/100-4        16.7kB ± 0%    15.2kB ± 0%   -8.92%  (p=0.000 n=10+10)
Microservice/1000-4        134kB ± 0%     161kB ± 0%  +20.40%  (p=0.000 n=10+10)
Microservice/10000-4      1.29MB ± 0%    1.76MB ± 0%  +36.56%  (p=0.000 n=10+10)
Microservice/100000-4     12.8MB ± 0%    17.6MB ± 0%  +37.57%  (p=0.000 n=10+8)
Microservice/1000000-4     128MB ± 0%     176MB ± 0%  +37.64%  (p=0.000 n=9+10)

name                    old allocs/op  new allocs/op  delta
Microservice/0-4            0.00           0.00          ~     (all equal)
Microservice/1-4            9.00 ± 0%      9.00 ± 0%     ~     (all equal)
Microservice/10-4           73.0 ± 0%      73.0 ± 0%     ~     (all equal)
Microservice/100-4           705 ± 0%       706 ± 0%   +0.14%  (p=0.000 n=10+10)
Microservice/1000-4        7.01k ± 0%     7.02k ± 0%   +0.14%  (p=0.000 n=10+10)
Microservice/10000-4       70.0k ± 0%     70.2k ± 0%   +0.19%  (p=0.000 n=10+10)
Microservice/100000-4       700k ± 0%      702k ± 0%   +0.20%  (p=0.000 n=10+10)
Microservice/1000000-4     7.00M ± 0%     7.02M ± 0%   +0.20%  (p=0.000 n=10+10)

[codecov-io]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #3   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          45     32   -13     
=====================================
- Hits           45     32   -13

Impacted Files	Coverage Δ
stack.go	100% <100%> (ø)	⬆️

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