Define gem specification files without `$/`
Add missing utf-8 encoding comment
Remove old rubocop configurations
Generate `.rubocop_todo.yml`

$ rubocop --auto-gen-config
Add .rubocop.yml
Clean Rakefile
RuboCop: Style/HashSyntax: EnforcedStyle: hash_rockets
RuboCop: Enable Lint/UnusedBlockArgument and Auto-correct
RuboCop: Enable Lint/UnusedMethodArgument and Auto-correct
RuboCop: Configure Style/Collectionmethods
RuboCop: Enable Style/EmptyLinesAroundBody and Auto-correct
RuboCop: Enable Style/PercentLiteralDelimiters and Auto-correct
RuboCop: Enable Style/SignalException
RuboCop: Enable Style/SingleSpaceBeforeFirstArg and Auto-correct
RuboCop: Enable Style/SpaceInsideHashLiteralBraces and Auto-correct
WIP
RuboCop: Enable Style/SpecialGlobalVars
RuboCop: Enable Style/StringLiterals and Auto-correct
RuboCop: Enable Style/UnneededPercentQ and Auto-correct