Use a flat crate structure so this git repo can store multiple (interconnected) crates in a single workspace

[JackKelly]

My plan is to write multiple, interconnected crates. Each crate will be fairly small, and each crate will operate at a single level of abstraction. These crates will be hosted in this git repo, in a flat crate structure.

I haven't completely figured out exactly how to divide the work between these crates. And the names of the crates will almost certainly change!

Ruff and Polars use a flat crate structure. As do many other projects.

UPDATE: The planned design has been moved to planned_design.md.

Relevant links

• matklad's blog post: Large Rust Workspaces
• Rust Programming Language book: Cargo Workspaces
• Rust Design Patterns book: Prefer Small Crates