https://developer.apple.com/reference
  https://developer.apple.com/reference/swift
    https://developer.apple.com/reference/swift/int
  https://developer.apple.com/reference/foundation
    https://developer.apple.com/reference/foundation/filemanager

Initialization and argument labels:
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html#//apple_ref/doc/uid/TP40014097-CH18-XID_272

https://swift.org/migration-guide/
http://blog.udacity.com/2016/04/getting-ready-for-swift-3-0.html

shell:
https://github.com/kareman/SwiftShell/blob/Swift3.0/Sources/SwiftShell/Bash.swift