Introduce egeloen/http-adapter (road to PSR-7)

This PR is a proposal for #344. 

I have removed the previous adapters but maybe we should keep and deprecate them. Let me know your feeling about it.
IMO, removing the interface is not a good idea due to the `GeoIP2Adapter` which still need to implement it and typehinting the Ivory http adapter once would force me to implement a lot of methods which are not really needed for it. I can obviously typehint just this class and let the `GeoIP2Adapter` as it is currently or not implement any interface at all for it but it would not be consistent.