[Orgmode] Improved org-timer-set-timer

[Bastien]

Hi all,

I've improved `org-timer-set-timer' again:

,----[ `org-timer-set-timer': new prefix argument. ]
| Called with a numeric prefix argument, `org-timer-set-timer' uses
| this numeric value as the duration of the timer.
| 
| Called with a `C-u' prefix argument, use `org-timer-default-timer'
| without prompting the user for a duration.
| 
| With two `C-u' prefix arguments, use `org-timer-default-timer'
| without prompting the user for a duration and automatically
| replace any running timer."
`----

The thing we need now is a way to display the timer in the modeline.

Thanks for Frédéric Couchet for ideas in this direction.

-- 
 Bastien