fossils as tips addition

R script for performing simulation tests where fossils are treated as tip taxa and models are fitted to data using Maximum likelihood. For space and clarity, simulations under different models have been added to a single script and commented out, such that individual models can be uncommented and run as required. It should also be noted that this script was written to be used on a cluster and thus to be distributed to many nodes at a single time. Users without access to a cluster may wish to loop this script multiple times if attempting to replicate results, but should take care not to overwrite previous results.