Robinson-Foulds distance calculations not consistent with Kuhner-Yamato

[ArtPoon]

See issue #85

[ArtPoon]

In brief, our implementation (and others) are consistently giving half the distance of the Kuhner-Yamato implementation.

[ArtPoon]

Making this low priority, let's not expend too much resources into diagnosing someone else's implementation of RF distance

[gtng92]

We did not actually implement RF.dist, KF.dist, and path.dist metrics. We used the package phangorn for this. Phangorn requires the igraph library to be re-compiled when bringing in this package (even though Kaphi itself has already compiled igraph). Would it be better simply to re-implement these distances again ourselves?

[ArtPoon]

For now use phangorn. Let's see how useful these distances will be before we think about re-implementing anything.