add SmartCodable

[iAmMccc]

Thanks for your contribution! This is a template that can make it easier when submitting your contribution:

Your Project: _ SmartCodable _
Project URL: _ https://github.com/iAmMccc/SmartCodable_
Category: _ JSON_
Description: _ Flexible and powerful Swift Codable system with support for type compatibility, transformers, custom wrappers, and more._

Inclusion requirements:

• Has 50 GitHub stargazers or more
• Only one project/change is in this pull request
• Isn't an archived project
• Has more than one contributor
• Has unit tests, integration tests or UI tests
• Addition in alphabetical order (bottom of category)
• Supports iOS 12 / tvOS 10 or later
• Supports Swift 4 or later
• Has a commit from less than 2 years ago
• Has a clear README in English

❤️ Awesome iOS Contributors

[vsouza]

Hi @iAmMccc. Please remove the empty line after project url.