CSV Support

**Is your feature request related to a problem? Please describe.**

Not exactly a problem, but our use case is generally "gather license information and put it in a spreadsheet" so this would be solving a problem for us for sure.

**Describe the solution you'd like**

It'd be super rad if there was an option to output CSV format instead of HTML.

**Describe alternatives you've considered**

We've used cargo-license for this in the past, but it would be nice to have it all in one tool and cargo-about / cargo-deny are really the direction we'd like to stick with given their feature set outside of this.