- Added support for functional indexes when using the

- Added support for functional indexes when using the
:meth:`.Operations.create_index` directive.   Within the list of columns,
the SQLAlchemy ``text()`` construct can be sent, embedding a literal
SQL expression; the :meth:`.Operations.create_index` will perform some hackery
behind the scenes to get the :class:`.Index` construct to cooperate.
This works around some current limitations in :class:`.Index`
which should be resolved on the SQLAlchemy side at some point.
fixes #222