title: How is CommonCrypto used in SWIFT3?
body: <p>The guidance is to to use #import "CommonCrypto/CommonCrypto.h" in the bridging header. This is from the question at: <a href="https://stackoverflow.com/questions/25388747/sha256-in-swift">SHA256 in swift</a>.<br>
  However, when I use the answers given by Andi and Graham Xcode still complains about "use of unresolved identifier CC_SHA256_DIGEST_LENGTH..."</p>
  
  <p>I am thinking I've made one of two mistakes: Either 
  (a) I am missing something in not having wired up the header and import correctly. i.e. I did not setup the bridging header correctly. I'd love clear steps on how to include the library and create the bridging header correctly. Or
  (b)The library is not included by default and I actually need to download it and store locally before I can use it. I'd love instructions on that.</p>
  
  <p>Thanks.</p>