Add a MaxDelay option

[lebauce]

This option ensures the delay between 2 retries can not exceed a specified duration

[codecov-io]

Codecov Report

Merging #28 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
+ Coverage   97.75%   97.87%   +0.11%     
==========================================
  Files           2        2              
  Lines          89       94       +5     
==========================================
+ Hits           87       92       +5     
  Misses          2        2

Impacted Files	Coverage Δ
options.go	100% <100%> (ø)	⬆️
retry.go	96.55% <100%> (+0.12%)	⬆️

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[JaSei]

Thank you for your PR.