Enable rubocop.
Merge pull request #6 from yasuhito/master

Master
Fix empty lines warnings.
Fix ascii comments errors.
Fix documentation error.
Fix FavorUnlessOverNegatedIf errors.
Fix NumericLiterals error.
Fix SpaceInsideBrackets error.
Fix SpaceInsideParens error.
Fix SpecialGlobalVars error.
Fix GlobalVars error.
Fixed all rubocop errors.
Merge pull request #7 from yasuhito/feature/rubocop_refactoring

Feature/rubocop refactoring
Merge branch 'release/0.2.0'