Binary targets are executable programs that can be run after being compiled. 
The default binary filename is `src/main.rs`, which defaults to the name of 
the package. Additionally one or more binaries are stored in the [`src/bin/`
 directory][package layout]. In this case the default binary `src/main.rs` 
is not required. The settings for each binary can be [customized] in the
`[[bin]]` tables in `Cargo.toml`.