https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/
https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/
. https://www.weheartswift.com/variables-constants-basic-operations/
. https://www.raywenderlich.com/143771/swift-tutorial-part-1-expressions-variables-constants
. https://www.hackingwithswift.com/read/0/overview
. https://github.com/matteocrippa/awesome-swift
. https://github.com/Alamofire/Alamofire
. https://github.com/onevcat/Kingfisher
. PUBLIC APIS: https://github.com/toddmotto/public-apis
. https://codelabs.developers.google.com/codelabs/firebase-ios-swift/#0