Plural and Parametrized keys

Adds support of plural and parametrized keys (issue https://github.com/webpack-contrib/i18n-webpack-plugin/issues/1).

The modern version of https://github.com/webpack-contrib/i18n-webpack-plugin/pull/42

Codecov Report

Merging #58 into master will increase coverage by 0.92%. The diff coverage is 96.52%.

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
+ Coverage   95.12%   96.04%   +0.92%     
==========================================
  Files           4       25      +21     
  Lines          82      354     +272     
  Branches       23      144     +121     
==========================================
+ Hits           78      340     +262     
- Misses          4       13       +9     
- Partials        0        1       +1

Impacted Files	Coverage Δ
src/interpolate.js	0% <0%> (ø)
src/pluralRules/pluralRule02.js	100% <100%> (ø)
src/pluralRules/pluralRule04.js	100% <100%> (ø)
src/pluralRules/pluralRule07.js	100% <100%> (ø)
src/pluralRules/pluralRule12.js	100% <100%> (ø)
src/pluralRules/pluralRule08.js	100% <100%> (ø)
src/pluralRules/pluralRule13.js	100% <100%> (ø)
src/pluralRules/pluralRule00.js	100% <100%> (ø)
src/pluralRules/pluralRule11.js	100% <100%> (ø)
src/pluralRules/pluralRule15.js	100% <100%> (ø)
... and 33 more

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smirks @d3viant0ne :)