Add workspaces for ww_net and ww_proc.

[lthibault]

This PR sets up two workspaces in Cargo.toml:

• ww_net
• ww_proc

The contents of src/net is move to ww_net/src.

src/proc contains a partial implementation of a process using Wasmer. It contains build-hooks to generate capnp schemas.

This is a refactor. There are no functional changes to the top-level application. The intent is to start separating out our main code components. Expect things to continue moving around a bit.

[mikelsr]

@lthibault I added some type gymnastics to be able to implement the Dialer trait. It's not an elegant solution, but AFAIK it's the only way of implementing traits for external types (I don't yet know much about rust so take it with a big grain of salt).

It's missing generics in the new type, if we decide this is the way to go we should add them on the next commit: add generics to DefaultSwarm(swarm::Swarm<ww_net::DefaultBehaviour>) making it DefaultSwarm<T>(swarm::Swarm<T>) or something like that.

[lthibault]

Thanks for the fix, Mikel!

I get the feeling I'm shaving against the grain with this Dialer trait. I wonder if there's a simpler approach (or at least an approach that's more aligned with the Rust way of doing things).

Let me play around with this a bit before merging :)