Featuretags

This closes #272

Rollup of commit logs:

    Add tag parsing logic from scenarios up to the feature as well.  Also
    extends a unit test to cover a scenario that we ran into where tags
    would break when the previous scenario ended with a table.
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    CLI now accepts @ for the tag argument without failing.  This was more
    because I'm lazy and didn't want to update all our CI runners that I had
    set up for my pull request, but also because I think it's nice to have
    the option of doing both.  Many people I've talked to consider the tag
    to include the '@'
    
    I also added a very basic test that covers the cascading of tags from
    feature to their child scenarios.  Hope it's helpful, and I really hope
    I have the chance to get back to submitting on it