Implement react-router 4

[diegohaz]

Closes #161

[codecov-io]

Codecov Report

Merging #227 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #227   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          41     41           
  Lines         277    277           
  Branches       54     54           
=====================================
  Hits          277    277

Impacted Files	Coverage Δ
src-example/components/atoms/Button/index.js	100% <ø> (ø)	⬆️
...le/components/molecules/PrimaryNavigation/index.js	100% <ø> (ø)	⬆️
src-example/components/atoms/Link/index.js	100% <100%> (ø)	⬆️

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