CLI: Configuration file names

I notice in https://gist.github.com/Gankra/d9ffe2cde001c6a615a3a9cf3928cddf, you mention the following filenames:

```
config.toml: your project-private configuration, similar to Cargo.toml
audits.toml: your audits and auditing-criteria, ready to be checked and shared
imports.lock: the audits you've imported from other organizations, similar to Cargo.lock
```

I think we'd benefit from naming these somewhat differently both for differentiation and for grouping, something like: `vet.toml` `vet-audits.toml` `vet.lock`.