Continue work on decorator usage.

Remove the need for wrappers.py now that there is an advanced
decorator provided that can provide all the same features as
the functor wrapper task class. This new decorator is now used
in the tests instead of the previous usage of the functor task
class.
Update how the version task functor attribute is found
Merge pull request #28 from harlowja/no-functor-task

Continue work on decorator usage.