Allow for multiple levels of tagging

[steveswinsburg]

XBDD only allows for one level of tagging.
If I have multiple feature files that related to each other, it would be nice to be able to tag each with multiple related tags to have them grouped.

For example, I tag a feature with the following two tags
@australia @nsw

And another with:
@australia @Tasmania

It would be nice if XBDD grouped these in a nested structure, such as

• Australia
  -- NSW
  -- Tasmania

Currently, I get them all as separate tags:

• Australia
• NSW
• Tasmania

All as separate tags.