Create analyse.rwty

This is a first attempt at a function that will essentially
automatically run all of the analyses most people will want from RWTY.
Various fixes to load.trees

Added functionality to make it take non-nexus tree format.  Also added
bits to make it unroot trees.  Because testing for rootedness is
time-consuming on large tree files, I've set it up so that it just
checks the first tree in the file and assumes that are all unrooted or
rooted if that one is.
Disable debugging printouts in slide.freq

Just reducing the overall clutter when analyse.rwty is run.  Can be
re-enabled at will, maybe at some point we should hook all of these
messages to a "verbose" option or something.
Testing load.trees function

Just added a line to test the load.trees function.  Soon we need to
rewrite these initial bits to use load.trees instead of read.nexus.
Disabled debugging code

Just turning off the tracking code to make analyse.rwty less messy
during execution.  Again, we might want to hook this to a "verbose"
option eventually.