[AUCTeX] style file for tabu package

[Mandar Mitra]

I've started putting together a very basic style file for the tabu
package. It's available at http://www.isical.ac.in/~mandar/tabu.el.

I haven't done this sort of thing before, so I don't know if it's any
good. I'd be happy to work on it some more if the admins think it could
become sufficiently useful to be included in a future release.

Grateful for any feedback.