• Add optional package checksum support. When a package URL is annotated with
  an MD5 checksum, ruby-build will use it to verify the contents of the
  downloaded file. Package URLs in all existing definitions have been updated
  with checksum annotations
• Add an optional package download cache. When the RUBY_BUILD_CACHE_PATH
  environment variable is set to a directory of your choice, ruby-build will
  store downloaded packages there and reuse them for future installations
• Add mirror support for faster package downloads. Packages on the official
  ruby-build mirror will be served via S3. You can point ruby-build to your own
  local package mirror by setting the RUBY_BUILD_MIRROR_URL environment
  variable