Swift framework wrapping CommonCrypto's SHA256 methods.

This is experimental. Do not use this in a production system.

1. Add the SHA256-Swift project to your existing project either through a workspace or as a subproject.
2. Link the appropriate framework (either SHA256iOs or SHA256Mac).
3. Where required, import SHA256iOs
4. In your main project, add the path to the CommonCrypto module directory to your Swift import paths. ${SRCROOT}/SHA256-Swift/CommonCrypto for example.