Add new status code mapper handler impl

[izumin5210]

To close #6

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 1.39%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #9      +/-   ##
=======================================
+ Coverage    82.6%   84%   +1.39%     
=======================================
  Files           3     3              
  Lines          46    50       +4     
=======================================
+ Hits           38    42       +4     
  Misses          7     7              
  Partials        1     1

Impacted Files	Coverage Δ
handlers.go	96.77% <100%> (+0.47%)	⬆️

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