es6, add tests, packaging updates

[msimerson]

• chore(ci): update with shared GHA workflows
• chore(ci): adjust codeclimate config
• chore(test): added tests for date_to_str, in_array, indexOfLF
• doc(README): fix badge URLs
• style: replace indexOf with includes (es6)
• style: replace for (i) with for..of
• style: _pad uses str.padStart (avail since node 8)

[codecov[bot]]

Codecov Report

Merging #24 (32b5dbd) into master (6032405) will increase coverage by 1.27%. The diff coverage is 94.28%.

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
+ Coverage   90.90%   92.18%   +1.27%     
==========================================
  Files           1        1              
  Lines         165      320     +155     
  Branches       33        0      -33     
==========================================
+ Hits          150      295     +145     
- Misses         15       25      +10     

Impacted Files	Coverage Δ
index.js	92.18% <94.28%> (+1.27%)	:arrow_up:

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