Merge pull request ishkawa#260 from ishkawa/release/4.0.0

Set version 4.0.0

Merge pull request ishkawa#254 from ishkawa/release/3.2.1

Set version 3.2.1

Merge pull request ishkawa#252 from ishkawa/swift-4

Xcode 9 / Swift 4

Merge branch 'master' into develop/4.0

Merge pull request ishkawa#224 from ishkawa/release/3.1.2

Release 3.1.2

Merge pull request ishkawa#219 from ishkawa/release/3.1.1

Release 3.1.1

Merge pull request ishkawa#216 from ishkawa/release/3.1.0

Update version to 3.1.0

Merge pull request ishkawa#211 from ishkawa/release/3.0.0

Release 3.0.0