[Ml-yokadi] Summary of recent changes

[Aurélien Gâteau]

Hi again,

I got a bit creative these last two days and made a few changes to 
Yokadi which I would like to present to you:

# t_list --done
"t_list --done" now takes a parameter to specify the range. For now you 
can use the following range keywords (hopefully self-explanatory):
- today
- thisweek
- thismonth
- all

I hope you like this one Simon :)

I am still not sure about the range keywords and it may be a good idea 
to have a syntax similar to the one Sébastien introduced in t_set_due. 
Feel free to suggest ideas.

# Negative urgency
You can set urgency to a negative number now. I find it useful to enter 
notes, that is: stuff I want to remember but I do not intend to mark 
done at some time. Having a negative urgency means these notes stay at 
the bottom of the task list.

# Refactoring
I created dateutils.py and moved some code from utils.py and taskcmd.py 
(t_set_due code) to it. Next: unit-tests :)

# t_mark* and t_remove
t_mark* and t_remove now print the title of the modified task. t_remove 
now prompts for confirmation, unless you specify the '-f' option.

Aurélien