Upgrade to AFNetworking 2.0

Morning.

I'm trying to use your pod in an app but I've run into a problem; I'm using AFNetworking 2.0 so I'm getting pod version conflicts.

Here's a changeset that upgrades the version of AFNetworking from 1.xx to 2.xx - unfortunately this also means that it's not iOS 6 compatible anymore because I used the NSURLSession subclasses. My use case doesn't have any need for iOS 6 compatibility; I don't know how important that is for your users - I guess if it is important then I could tweak this to use the iOS6 compatible bits of AFNetworking?

I've submitted it in two commits - the first (1114303) does the actual work (including a change to the .podfile I'm afraid, I had to up the version number in the dependency).

The second commit (67c2d2b) is just me upping the version number in the podfile (to 2.0.0) and tweaking the readme. This is just I can use this pod in my app right away - it's got nothing of value in, I'd cherry-pick it out :)

I've tried to follow a your coding style but it's very different to mine so I might have got some of it wrong. Sorry :)

Anyway, let me know what you think - I appreciate that this is quite a breaking change so if that's not what your users want then reject this :)

Sam