The fitting function used by pmc to generalize fitting to both geiger and ouch models.
pmc_fit(tree, data, model, ...)
the object returned by the model fitting routine (gfit for geiger, hansen/brown for ouch)
a phylogenetic tree. can be ouch or ape format
trait data in ape or ouch format
the name of the model to fit,
whatever additional options would be provided to the model fit