Create tree.distmatrix.R

New function and file for calculating a matrix of RF distances between
trees within a chain.  At present it's doing this in a very slow and
silly way, but it works for testing purposes.
streamlining tree.dist.matrix.R

Made the function more generally usable, deleted some extra debugging
code.
New RWTY.R, loads tree dist matrix
Ancillary non-working functions in progress

added a skeleton for the tree space plotting function in plawty.R, and
the start of a function to create treespaces from a list of multiphyolo
objects