finding cycles in directed graph

My graph theory's a little rusty, so it might be easy to do using the provided API, but is there an easy way to get a list of all the cycles (either as new `Graph`s, or as edgelists) in a directed graph?

`is_cyclic/1` can tell me if there _is_ a cycle, but I want to know what the actual cycles are (I realise this is computationally expensive, that's fine because I only care about small graphs).