Log Message:
Updated todoman to 3.1.0.

v3.1.0
------

* Last-modified fields of todos are now updated upon edition.
* Sequence numbers are now properly increased upon edition.
* Add new command ``todo cancel`` to cancel an existing todo without deleting
  it.
* Add a new setting ``default_command``.
* Replace ``--all`` and ``--done-only`` with  ``--status``, which allows
  fine-grained status filtering. Use ``--status ANY`` or ``--status COMPLETED``
  to obtain the same results as the previous flags.
* Rename ``--today`` flag to ``--startable``.
* Illegal start dates (eg: start dates that are not before the due date) are
  ignored and are removed when saving an edited todo.