Add ignore-commits-with option to filter commits with ignored words

[alexcanessa]

Resolves #84

[codecov-io]

Codecov Report

Merging #103 into master will decrease coverage by <.01%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage   80.69%   80.68%   -0.01%     
==========================================
  Files           7        7              
  Lines         347      352       +5     
==========================================
+ Hits          280      284       +4     
- Misses         67       68       +1

Impacted Files	Coverage Δ
lib/_options.js	83.33% <0%> (-16.67%)	⬇️
lib/src/Gren.js	78.05% <100%> (+0.37%)	⬆️

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