Merging changes across rwty2-rob and master branch

We've had two different people add new tree distance metrics to two different branches - Martin Smith on the master branch for RWTY 1 and Michelle Kendall on Rob's branch for RWTY 2.  There's some duplication of functionality there but there are also differences.  When we do get around to a development push for RWTY 2 we're going to have to do a little bit of work to merge those changes together.