Update to prepare for iOS 7 and clean a bit the project.

* Updated Facebook iOS SDK to 3.7.1.
* Replaced Facebook iOS SDK sources with FacebookSDK.framework in Xcode project.
* Setup build.xml and platform.xml to package FacebookSDK.framework with the ANE.
* Setup Facebook iOS SDK as a git submodule for easy update.
* Migrated Xcode project to ARC.
* Reorganized Actionscript folder to have only one project.
* Updated the ASDoc.
* Updated extension.xml and platform.xml for AIR 3.8.
Merge branch 'master' into develop

Conflicts:
	bin/AirFacebook.ane
Updated README