Project and code reorganization

Hello, Mattt. 

Congratulations for the excellent work you have been doing (in this and all your other projects). I would like to say thank you on my behalf and, I believe, on behalf of the whole community of developers! :-) 

About the Alamofire library, I think that sooner or later it will need to undergo a restructuring to facilitate the understanding, use and future development. Perhaps the best time is now, before start popping other pull requests. 

This PR may be a starting point for this (assuming that I understood the development line correctly).

What do you think?

Kind regards, 

Van