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).

No files, tests, or entry points are named. Start by mapping the library's interfaces and their current parsing and IO responsibilities, using the linked HTTP/1.1 example and PyCon talk for context. Done means parsing and IO are clearly separated for each interface while preserving the library's external behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.