Update Plug with Versioned Doughnut

[mzxyz]

• Refactor Plug to use the new versioned Doughnut enum type
• May require creating and tagging a new release branch for doughnut-rs (includes Cargo.toml version bump)

This should be part of the Plug and CENNZnet 1.0.0-rc2 releases

[mzxyz]

Actually this one is more complicated than I though.

plug-blockchain/prml/doughnut/src/lib.rs

Line 40 in 0966e9d

pub struct PlugDoughnut<Doughnut: DoughnutApi, Runtime: DoughnutRuntime>(Doughnut, rstd::marker::PhantomData<Runtime>);

In doughnut PRML, Doughnut type has trait bound DoughnutApi, which current versioned doughnut has not implemented.

plug-blockchain/bin/node/runtime/src/lib.rs

Line 124 in 0c18345

type Doughnut = prml_doughnut::PlugDoughnut<Doughnut, Runtime>;

So in the runtime implement, there will have problem if we used versioned doughnut directly

[cowboy-bebug]

We have trouble with the associated types for DoughnutApi trait because PlugDoughnut struct takes Doughnut: DoughnutApi as type parameter -> we have to impl DoughnutApi trait for the (versioned enum) Doughnut. We're not sure how to go about defining the associated types for Doughnut (whether to make it generic or remove associated types for fixed types).

A task for this is open here: cennznet/doughnut-rs#38

[jordy25519]

I think the DoughnutApi trait should be moved so that it is defined here in Plug instead of doughnut-rs. It should only be implemented for PlugDoughnut which can then handle the version management internally.