Support Prost 0.7.0

[wchargin]

Feature Request

Upgrade to support Prost 0.7.0.

Crates

All.

Motivation

Prost 0.7.0 is now out. It includes general improvements, like
support for zero-copy deserialization of bytes fields, as well as
improvements of specific interest to Tonic, like support for file
descriptor sets to support gRPC reflection.

Applications that use Tonic cannot easily upgrade Prost until Tonic
itself is updated. (When I try to make the obvious change in my
downstream project, I get a slew of trait bound errors because of the
duplicate versions of prost::message::Message.)

Prost 0.7.0 depends on bytes = "1", so this may be blocked on
upgrading to v1 of the Tokio ecosystem.

[djc]

This was done, as part of #530.

[wchargin]

Sweet! Thanks @djc for the heads up and thanks to everyone on #530,
#514, and related work for the quick implementation here.

Looks like releasing is probably covered by #443, so I’ll close this.