Packaging Rust crates in GNU Guix

Not much people who're familiar with Rust, apparently (at least at the time of the talk). Nonetheless, Rust-based tools are included.
Created an importer using the Crates.io API. With the importer, it can recursively build the module all the way down (most of the time).
It pulls all of the dependencies. The side effect is that every package has to be defined. The importer just makes it easier.
The community have a preference to shared libraries and sources. Vendoring is not much of a popular option. Since Rust downloads everything and the community wants to reuse the components, it seems the solution is to package everything.