conn: deprecate Halt() #29
Description
Ported from google/periph#377.
Move the blocking operation context from the driver to the individual function call.
See https://docs.google.com/document/d/1vQdZdoOMaIan7dKwcAzqHbfM_LCnnSMUQvqypRkjohM for more information.
As such, Halt() will not be needed anymore.
This is a big deal, but the rationale is that it will tremendously simplify the device drivers. Most people get this wrong, and it had been a point of friction for contributors and obscure for users.