Add ReerCodable

[Asura19]

• Project Name: ReerCodable
• Project URL: https://github.com/reers/ReerCodable
• Project Description: Codable extensions using Swift macro.
• Why it should be added to awesome-swift: It use macros to make serialization simpler with declarative annotations.
• 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 🤓