Cargo is a tool that allows Rust projects to declare their various
dependencies, and ensure that you'll always get a repeatable build.

To accomplish this goal, Cargo does four things:
- Introduces two metadata files with various bits of project
  information.
- Fetches and builds your project's dependencies.
- Invokes rustc or another build tool with the correct parameters to
  build your project.
- Introduces conventions, making working with Rust projects easier.
