0.4.0

Changed

• Repository renamed from ResponsiveLayoutKit to swift-responsive-layout
  (https://github.com/KalebCooper/swift-responsive-layout), following the
  swift-* package naming convention. The package manifest name is now
  swift-responsive-layout. The library product and module remain
  ResponsiveLayoutKit, so import ResponsiveLayoutKit is unchanged.
  GitHub redirects the old URL, but update .package(url:) and any
  .product(name:package:) references (package: "swift-responsive-layout").
  The DocC site now lives at
  https://kalebcooper.github.io/swift-responsive-layout/.
• Xcode scheme is now swift-responsive-layout (auto-generated from the
  manifest name). CI, the PR template, and CONTRIBUTING reference the new
  scheme name.