Changes to allow easier inclusion in other projects.

Thanks for making this!  It's great - really useful.

I'm using this in another project as a Git submodule, so I made a few changes to allow it to use the static library more easily:

- Change the SDK to Xcode default - allows compilation with Xcode 4.6.
- Copy the headers when building the library so that they can be used in superprojects including this project as a submodule.
- Add new "FCEasingAnimation.h" header that includes other headers, to allow "#import <FCEasingAnimation/FCEasingAnimation.h>" to work when using the library in other projects.