Merge pull request raspu#80 from woxtu/spm

Add Swift Package Manager support

Update README.md

Swift 4.2, lighter assets, dependency injection

Using fonts without an italic variation is now supported

Ported to Swift 4, highlighter.js updated to 9.12.0

Added automatic language detection, highlighter.js 9.9.0

Updated for Swift 3.0, highlighter.js 9.8.0

highlight.js updated to 9.6.0, fixed raspu#4

highlight.js updated to 9.5.0

CodeAttributedString refactoring, bugfixes, documentation