Docs of stagger and step

@awage I worry that the docs of the stagger and step function are incomplete. The docs specify that the `isinside` function must define a region with no attractors. But that's not all, right? I think it must contain the chaotic saddle one wants to find...? And does it have to contain the saddle fully, or just a part of the saddle is enough? In addition, does this function also work for continuous time systems? In the docs time is always worded as discrete time.