0.5.0

• This release is tested with Bazel 0.20.0.
• Support linking prebuilt framework dependencies (objc_framework and the new apple_framework_import rule in rules_apple) into swift_{binary,test} targets.
• Allow Objective-C rules to depend on swift_import targets.
• Add alwayslink support to swift_{binary,test}.
• Add -pie flag when linking on Linux.
• Add descriptive progress messages to most actions.
• Add dependency on bazelbuild/apple_support.