Use Google error-prone in reports

[DavidWhitlock]

The error-prone tool from Google looks interesting: https://github.com/google/error-prone

I should add it to the reports that are generated for the site.

[DavidWhitlock]

Interesting. error-prone is configured by modifying the compiler configuration in Maven: https://errorprone.info/docs/installation

And it requires that a bunch of add-exports be configured in .mvn/jvm.config.

That might be okay for my own code, but it's probably to much for the students.