Change type of exclude property to csv

[leorossi]

exclude property is a comma-separated string of values, which are parsed to an array internally.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Fixes: #53

[simoneb]

Let's wait for a reply on #53 (comment)