Add support for async steps.
Basic support for scenario outlines

The primary shortcoming of this implementation is that
it generates scenarios using the outlines at parse-time,
which results in the ecukes output being the scenarios
rather than the outlines that cucumber proper would
print out.

But if you really want scenario outlines, like I did,
this is better than nothing!
Merge branch 'async'
Merge branch 'scenario-outlines'
Update copyright year.
Add Kyle Hargraves as contributor.
Update version to 0.4.0.