For v2.0
--------

- CHECK: lines 100-102 of RecursiveSymmetryCutBase.hh: this was
  initially setting the structure members to 0. I think it's highly
  preferable to set them to their default of -1, signalling the
  absence of substructure. [0 dR might happen with a perfectly
  collinear splitting]

- CHECK: are we happy with how the structure info is stored and the
  recursive_soft_drop_prongs(...) function in RecursiveSoftDrop.hh?

- QUESTION: do we move set_min_deltaR_squared in the base class?

- Add option to define z wrt to original jet?

For future releases?
--------------------
- JDT:  In Recluster, change "single" to an enum for user clarity?
  [do we have any other option that "sungle" or "subjets"]
- JDT:  Should we have a FASTJET_CONTRIB_BEGIN_NAMESPACE?  It would
  help those of us who use XCode to edit, which is aggressive about
  auto-indenting. [Consider this for the full contrib??]
- More generic kinematic cuts?
- KZ: common base class for IteratedSoftDrop and RecursiveSoftDrop?
- KZ: make IteratedSoftDrop use Recluster