Ticket #1303 (new enhancement)

Description

From Chris Godsil's wishlist and Robert Miller's reply:

>>> (b) Cayley graphs: These can be dealt with in GAP, but I think it would be
>>> useful to have a class, with the group and generating set explicit. Cayley
>>> graphs could be directed or undirected. Circulants and Cayley graphs
>>> for Zd (where p is prime) could be useful special cases.
> Cayley graphs are implemented, but most likely not to the extent
> anyone wants. For example, you can call cayley_graph on some groups,
> and get the graph back, but the functionality is very limited. There
> is certainly no CayleyGraph class, which would be a thousand times
> better than the current situation. Definitely create a ticket for
> this.