[Dune] Grid Documentation

[Christian Engwer]

Hi,

I thought about the comments on my last Doxygen mail. I also found a
lot of funy features in doxygen and I rewrote again the
documentation. Please have a look at
http://hal.iwr.uni-heidelberg.de/~christi/dune
and let me know what you think. I removed the BlaGridSomething
groups. All Implementaions of the grid interface can now be found via
the GridDefault base class. I also instructed Doxygen to include the
inherited meber functions because otherwise we can't see what the
complete interface is.

Cheers Christian