Add ExtendedAttributes

[sindresorhus]

• Project Name: ExtendedAttributes
• Project URL: https://github.com/sindresorhus/ExtendedAttributes
• Project Description: Lets you easily manage extended attributes (file metadata)
• Why it should be added to awesome-swift: It lets you deal with extended attributes in a Swifty way instead having to deal with ugly unsafe C APIs.
• At least 15 stars (GitHub project)
• Support Swift 5
• Updated contents.json instead of README
• Lib is fully open sourced, written in Swift and not a wrapper over compiled lib
• Description does not say "written in Swift" or variant 🤓

[matteocrippa]

@sindresorhus thx for the submission!