Reset ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES flags.

[KelvinJin]

This pull request reset the ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES flag.

This flag will not cause problem if the user simply uses it during development and removes it from the final App Store bundle. However, when I use xcodebuild on the ci machine to archive my project that includes this framework, a weird libswiftRemoteMirror.dylib file will be included into the bundle. And ItunesConnect will reject this bundle. Check this question for reference.

This pull request also restructured how the framework is linked into the demo app. The demo app now can run without any issue in the latest Xcode 8.2+.

This PR won't effect the existing users.

BTW, if you check other libraries such as Alamofire/SwiftyJSON, they all set ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES to default value. So you can trust this decision.

Let me know if you need more information.