Initial attempt at adding Unified support.

Xamarin.iOS is failing with the follow error:
> Objective-C exception thrown.  Name: NSInvalidArgumentException ..... unrecognized selector sent to instance

https://www.dropbox.com/s/l7k43fheu79uj88/Screenshot%202014-11-21%2007.22.55.png?dl=0

Xamarin.Mac Unified is not working at all. Need to figure out what the #ifdef should be
Bumped version to 1.5 and updated Readme.
Merge pull request #8 from crdeutsch/unified

Added Unified Support