Add framework and Carthage support

[hankbao]

No description provided.

[ruslanskorb]

[pronebird]

I suppose this import will only work on framework, but hey what's wrong with good old include we had before?

[hankbao]

Oops... my bad. I've fixed that import statement and also updated the missing visibility setting of framework headers in f97786b.

[hankbao]

It seems there are still some building issues on Travis CI with the newly added protected header importing statement in the framework umbrella header. However, that protected header should be put there if we need to expose it to the framework users as I understand. Or should I mark it as the private header of the framework?

[hankbao]

As Travis CI is happy with recent commits now, hopefully this pr could be merged.

[abbysingh]

Hey is carthage support available in master now?