Feature request: expose the `excludeList`/`tag` to subclasses

[Brendon-Mendicino]

It would be nice if we could control which classes to exclude from the stack-trace. Some times this might be handy, think about some helper class/custom logger implementation, which wraps the calls to the actual log functions d/i/w/e, in such cases I would like to have a StackTraceElement that is one layer above the current wrapping call. This might be useful in general, especially if you instantiate "Proxy" objects that do some kind of logging inside.

Maybe DebugTree.fqcnIgnore could be made protected (or helper methods could be added), or tag might be made protected instead of internal, guaranteeing a complete control over how the tag is created, in such a way custom classes might create their own custom logic for how a tag is created/how the stack-trace is iterated over.