Reorganize project layout

[ishkawa]

We should support Swift 3 as soon as possible, but we encounter trouble in running CI jobs.
To resolve this, I have made following changes:

• Introduce Action.xcworkspace to build dependencies using git submodule.
  • Submodules are checked out by carthage update --use-submodules.
  • No tool update is required to follow Xcode update.
  • This layout is the same as that of ReactiveCocoa repository.
• Merge Demo.xcodeproj into Action.xcodeproj.
• Run CI jobs on Xcode 8.

[ishkawa]

@ashfurrow Thank you for reviewing this PR ✨

Could you release current master as 1.3.0? It may be the last version which supports Swift 2.x, and there're some merged PRs which is not contained in version releases.

[ishkawa]

I noticed RxSwiftCommunity does not have write access to this repository, is it intended? Some other repositories give write access to the organization, and I think that is better to keep repository active.

[ashfurrow]

Ah, no that's unintentional. Should be fixed now.

[ashfurrow]

Ok, cool. I'll release 95be402 (master as of this merge) later this afternoon.

[ishkawa]

Great 👍 Thank you!

[ashfurrow]

1.3.0 is released, is there any reason to wait before releasing a version for Swift 3?

[ishkawa]

Since the latest released of RxSwift for Swift 3 is still beta, I think our release for Swift 3 (possibly 2.0?) should also be beta.

[ashfurrow]

Makes sense. So I should release a 2.0.0-beta.1 you think?

[ishkawa]

Yes 👍

[ashfurrow]

Okay, pushed as 2.0.0-beta.1, let me know if you run into any issues, and thanks again!