OS X support

[raxcat]

Hey, finally found a new framework except Objective-Flickr.

I read issues and there were 2 issues #2 and #11 regarding to this.

But the pull request was not finished yet. Is there any problem out there.

I would like to help creating an OS X framework(with module support) and OS X demo app.

[raxcat]

Hey I fork the repo. And commit the first version of supporting OSX. raxcat@6e0026e

To prevent too much shimming(#If TARGET_OS_IPHONE) which would cause troubles maintaining code, I created DUImage in FKDataTypes.h just as previously discussed.

#if TARGET_OS_IPHONE
typedef UIImage DUImage;
#else
typedef NSImage DUImage;
#endif

Though, there are still some stuffs from AssetsLibrary would cause cross-platform issues. Cause there are few codes related to this, I just use shimming for AssetsLibrary related codes.

I also modified FlickrKit.h to support module(OSX). I did not modify anything regarding to iOS static library.

The OS X demo app does not demo well now. I am working on it.

BTW

FOUNDATION_EXPORT double FlickrKitOSXVersionNumber;
FOUNDATION_EXPORT const unsigned char FlickrKitOSXVersionString[];

will be changed to

FOUNDATION_EXPORT double FlickrKitVersionNumber;
FOUNDATION_EXPORT const unsigned char FlickrKitVersionString[];

in case the iOS library needs to support module, inspired by Alamofire swift frameworks (Actually the name doesn't matter but I will change them)