0.4.0

• Git deployments: scripts/vercel-install-swift.sh, used as a project's Install Command, installs
  the swift.org toolchain and Static Linux SDK in Vercel's build image and keeps them (and the
  package's .build) in Vercel's build cache, so Vercel can run swift package vercel on every
  push. See "Deploy from Git" in the README.
• swift package --disable-sandbox vercel init [build options] sets up Git deployments: it sets
  installCommand and buildCommand in vercel.json, creating the file if needed. In an
  existing vercel.json nothing else changes, not even formatting or key order.
• swift package vercel --swift-sdks-path <path> (or SWIFT_VERCEL_SDKS_PATH) builds with SDKs
  from another directory.
• vercel.json build settings (installCommand, buildCommand, ...) no longer print an
  "ignoring" note.
• Inside vercel build (VERCEL=1), crons are no longer copied into config.json: Vercel adds
  them from vercel.json itself and rejected the duplicates.