[dwm] on-the-fly tags creation and deletion

Trying to add more dynamism to the "d" in dwm I added the possibility
to add or removes tags while dwm is running.

You need the attached patch (for release 0.9 and up) and a script like
http://wiki.mad.mw/dwm/StartupScript to be able to communicate with
dwm. Feel free to use lower delay time.

Then, you can just add a new tag:

echo "add tag newtag" > ~/.dwm/status

or remove a existing one:

echo "del tag oldtag" > ~/.dwm/status

With the new tag approach I think this features are quite handy.

regards,

-- 
Julián
PS: it's not finished, I need to improve it to handle clients tagged
only with a tag being removed