Filter/exclude by genre

[sourcefrog]

Mutants now have a concept of 'genre', like BinOp, expressing the general category.

This is present in the json output but you can not yet easily filter by them.

Like the other filters it would make sense to allow this both on the command line and in the config file. It might also make sense to allow them within attributes in the source.

More on this in https://github.com/sourcefrog/cargo-mutants/discussions/258#discussioncomment-8214982