Added BPS screen event.
Added placeholders for screen context and event (libscreen)
Consolidated version testing (though more version testing functions have been added)
-Added tests for determining if something is capable of running
-Added ability to throw an exception if something isn't capable of running on the current OS version.
Changed Util.ThrowExceptionForErrno to Util.ThrowExceptionForLastErrno.
Added Util.ThrowExceptionForErrno where Errno can be passed into it.
Made DeviceInfo.OSVersion static
Nuspec file now referenced in project file.
Util.ThrowExceptionForErrno now throws meaningful exceptions.
Updated readme so it's formatted batter.