Should `%implements` map to `with`?

Currently, `%implements Foo` results in `implements Foo` being included in the class declaration line (see [ScalaEmitter.java:274](https://github.com/strubell/jflex-scala/blob/4ad9f781465acfc2cb5d9187980d96ee36b6f155/jflex/src/main/java/jflex/ScalaEmitter.java#L274)). Would it make sense to emit `with Foo` instead so that mixins could be specified with `%implements`?