Common.md

Common

Meant for library internal stuff:

• Swift 4 & 4.2 support code.
• Require

Require

Useful for replacing this:

guard let value = someValue else {
  fatalError("Missing someValue in ...")
}

With this:

let value = someValue.require("Missing someValue in ...")

Note: Only use this very sparingly! It's essentially a force unwrap with a nice message.