Added Compatibility of the Client Side Encryption Framework to Mac OS X 10.7 and higher

The encryption framework was not compatible to OS X. My contribution makes use of Security Transforms as suggested by Apple (https://developer.apple.com/library/mac/documentation/security/conceptual/SecTransformPG/SigningandVerifying/SigningandVerifying.html) in order to provide this compatibility.

On top of that, I changed the title in the README and added a description on how to use the SDK on Mac OS X.