Simulation testing

[ArtPoon]

• I've written a Python script to swap branches of an input tree at a certain depth - we can use this to simulate an alignment of recombinant sequences
• I'd like to simulate alignments with one or more recombination events, where the times of those events are distributed uniformly over the tree, which is equivalent to uniform over time weighted by the number of branches - this is more realistic than exchanging segments between extant sequences in an alignment.
• I'd also like to explore whether we can detect recombination events between parent lineages, one of which has no sampled descendants.