OAuthSwift allow to generate OAuth-signed URL requests AND send them with the networking library of choice

I read into readme :

```
OAuthSwift already provides a working client for creating and sending signed URL requests, however it does not provide a way to independently generate OAuth-signed URL requests AND send them with the networking library of choice (such as Alamofire or NSURLConnection).
```

This is no more true I think, but maybe I miss something when I try to achieve that
- some methods has been cut into many methods
- some methods are now public or extracted into a static one

I am planing to make a project named "OAuthSwift-Alamofire" so that's why I am here after looking on Alamofire+OAuthSwift

Start with the README and the current public or static OAuth request methods mentioned in the issue, then compare them with the Alamofire+OAuthSwift usage. Verify whether signed URLs can be generated independently of the built-in networking client. Done means the capability is either confirmed and documented or the missing API behavior is clearly specified.

Written by the indexing model from the issue text.