Update the Xcode configuration and the Rakefile

hi, I am an iOS developer, thanks for your kxMovie, it helps me a lot, so I decide to make it better, below are my changes
1.Modified the Rakefile, plx see the differ
2.Modified the Xcode configuration, now the ffmpeg libs and include filed for specific architecture lies in the same folder

Any questions, please contract me via email: kinglong_h@126.com