Add ability to create a string transport logger for testing #33

[tripodsan]

see #33

[codecov]

Codecov Report

Merging #41 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #41      +/-   ##
==========================================
+ Coverage   98.58%   98.64%   +0.05%     
==========================================
  Files          12       12              
  Lines         638      662      +24     
  Branches      147      150       +3     
==========================================
+ Hits          629      653      +24     
  Misses          9        9

Impacted Files	Coverage Δ
src/Logger.js	100% <100%> (ø)	⬆️

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