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.

[272]

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

[272]

Fix CLI exit code

The 'lettuce' CLI, after a successful test run, was always exiting with
an exit status of 1 indicating an error. The main() function was
erroneously considering the test run a failure if the TotalResult
instance returned by runner.run() evaluated to True (which is always
does).

This issue was reported on the mailing list [1] by Dave Sykes. I ran
in to the same problem while running lettuce from tox which reports the
success/failure of a test run based on the exit status of the test
command (lettuce).

[1] https://groups.google.com/d/topic/lettuce-users/6Nu2QXE1MBc/discussion

Add tox.ini for tox (http://tox.testrun.org/)

Fix for situation where 'localhost' is not resolvable

 * Scenario instances now have a `self.previous_scenario` attribute pointing to the last full-featured scenario (if any)
 * the runner now takes tag names
 * Scenario have now a method that matches strings