gtasks --match: Implement option for handline matching subtasks

[bjohas]

If the top level task matches, the whole task should be processed. If top task doesn't match, but a subtask matches, only the subtask should be moved.

[bjohas]

Issue #22 provides a more detailed approach to this. In resolving #22, need to make sure that string matching on subtasks works.

[bjohas]

Thanks for the options in #22. Let's assume we implement #22. as:

• The whole task (Task 1 + subtasks) should be presented to the pipeto (that's my preference, "--subtasks process_if_parent_matches")

I would say the only other version we need to cover (for now) is this:

• Task 1
  -- SubTask A
  -- SubTask B MATCH_STR

This could be an option called --matchsubtasks yes|no. If yes, the above SubTask B is presented to pipeto, otherwise it isn't.

However, that's not urgent.