Implemented HttpAdapter with guzzle

I'm gonna add some comments to the code, would like for you guys to let me know what you think about it.
@staabm I think that the fact that we cant think of a reason now, doesn't mean there won't be a reason to do it at some point. I agree that it is indeed unlikely, but nevertheless... Also, I'm using it inside the constructor, and I don't like accessing properties directly, even if inside the own class.

@GrahamCampbell You are totally right, I will change it.