Add Rubocop and Fuubar to development dependencies
Add Rubocop config files
Rubocop: allow Void enforcement
Fix some errors and dead code caught by void-context warnings
Rubocop: allow EndAlignment enforcement
Correct misaligned "ends" caught by Rubocop
Rubocop: allow AmbiguousOperator enforcement
Fix a couple of ambiguous uses of &block parameters
Rubocop: allow ConditionPosition enforcement
Fix "single line" conditionals that were broken into two lines
Rubocop: allow StringConversionInInterpolation enforcement
Remove superfluous #to_s usage in interpolated strings
Rubocop: allow DeprecatedClassMethods enforcement
Replace "deprecated" class method File.exists? with .exist?
Rubocop: allow SpaceBeforeFirstArg enforcement
Put space between methods and their arguments
Rubocop: allow Loop enforcement
Rewrite begin/end-while loops as loop-do/break-unless/end
Rubocop: in todo, set AssignmentInCondition to "AllowSafeAssignment: true"
Remove some assignments in conditions

Simplified some other conditionals at the same time