Added Utility method for topological sort

[michielmulders]

Provide utility method for topology sorting #113

[codecov-io]

Codecov Report

Merging #117 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #117   +/-   ##
======================================
  Coverage    82.2%   82.2%           
======================================
  Files          21      21           
  Lines         281     281           
======================================
  Hits          231     231           
  Misses         50      50

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[michielmulders]

Had to rewrite code a bit to fit eslint style.
I changed if (!!input.fulfills) { ... } to if (input.fulfills) { ... }

According to this rule: https://eslint.org/docs/rules/no-extra-boolean-cast ::

In contexts such as an if statement’s test where the result of the expression will already be coerced to a Boolean, casting to a Boolean via double negation (!!) or a Boolean call is unnecessary

[TimDaub]

Please add docs for this.

[michielmulders]

Moved to: #143