Rename binary to cargo-fix

[oli-obk]

After a cargo install rustfix, the subcommand cargo fix would be available.

[killercup]

Can we cheat and add two [[bin]] with "rustfix" and "cargo-fix" as names, but both with src/main.rs as target? :D

[oli-obk]

Cargo will produce

warning: file found to be present in multiple build targets: src/main.rs

if we do that :(

I guess we can move the logic to lib.rs and load it from both src/bin/rustfix.rs and src/bin/cargo-fix.rs which simply have the same source code. Or go the extremely hacky route of creating src/bin/cargo-fix.rs with the content include!("../main.rs")