Add callbacks (keitaoouchi#94)

* Add callbacks

* version++

Add MarkdownUI for SwiftUI (keitaoouchi#93)

* Add MarkdownUI for SwiftUI

* Add SwiftUI

* version++

Add remote stylesheet support (keitaoouchi#88)

Feature/add markdown body to container (keitaoouchi#87)

* Add .markdown-body to the container class

* Bump version

Bump version (keitaoouchi#86)

Update version (keitaoouchi#83)

Support SPM (keitaoouchi#59)

Dark mode support (keitaoouchi#58)

* Dark mode support

* update toolkits

* bump versions

* rebuild assets by latest toolsets

* update version

* fix supported xcode and swift versions

Remove .swift-version (keitaoouchi#39)

Support Swift4.2 (keitaoouchi#33)

* Support Swift4.2

* Bump version

* update .travis.yml

* fix osx_image