Split the parsing and the IO

I'm convinced we should clearly split the parsing and the IO for each interface. This obviously effects the entire library - but it should all be internal changes.

See [this http 1.1 example](https://h11.readthedocs.io/en/latest/basic-usage.html) or [this great pycon16 talk](https://www.youtube.com/watch?v=7cC3_jGwl_U).