0.6.0

• This release is tested with Bazel 0.21.0.
• Incompatible change: The resources and structured_resources of swift_library have been removed. Replace them as follows:
  • Files and labels referenced in resources can be placed directly in the library's data attribute.
  • Files and labels referenced in structured_resources should be moved to the structured_resources of a new apple_resource_group target (defined in rules_apple) and that target should be placed in the library's data attribute.