Ignores .DS_Store
Adds random research papers, to be deleted later
Introduces disjoint-set data structure

As required by Zwick (2013) p.9
Extracts new class `Visualize`
Extracts method `#dot`
Introduces semicolons in .dot files, for readability
Make one less temp. file, validate OS env.
Add tests: LabelSet
Add tests: Matching
Add DistinctArray, a poor-man's ordered set
Rely on global rspec configuration

Other people have different preferences.
Tidy test output a bit
Extract `Path`
Update development dep.s
WIP kusner