Netapp v0.5.0

Introduces an API to attach streams of data to requests and response.
This allows to transfer big blocks of data in a streaming fashion
and process them as they come on each end, instead of having to wait
for the full transfer to be done.

This release is a major refactor of Netapp, which should allow many
performance improvements. Netapp now supports easily cloning requests
that need to be sent to multiple nodes thanks to an intermediate struct
Req<M>. Netapp can also have an order tag attached to requests and
responses to indicate that several messages are part of a same logical
sequence of messages, and that they should be sent in that order
(sending them in a different order isn't bad but it's a sub-optimal use
of network resources).