0.24.0

Improvements:
— Make ios.colors, ios.icons, ios.images and ios.typography parameters optional (#106)
— Add support for iOS color grouping (#107)

Fixes:
— Fix floating point arithmetic for letter spacing tracking: 0.20000000049 becomes tracking: 0.2.
— Fix formatting of swift files generated using figma-export typography. Add new line at the end of a file.