Merging changes across rwty2-rob and master branch

[danlwarren]

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.