Let reports support the groupByClass option

[npo-mmenke]

Great library, thanks for doing this!

It would be nice if the different file reports would support the groupByClass option.

[floriankraemer]

Hey, thank you! Feel free to create a pull request with those changes. Please just make sure they are tested. Unfortunately this has a low priority for me at the moment, due to a lack of time. There are other things like adding caching.