Completed task update

[cyrakuse]

I never think about update task status and when i check it i have to go to files to update it.
It will a good feature to update the status directly from the list

[mikaeljorhult]

Yes, it's one of my first feature requests (#7) but I've never got around implementing it as I don't really use it myself.

I'll have another look once 0.6.0 is out.