set_posterior: Set an posterior to a file
In richelbilderbeek/wiritttes: WIRITTE simulation

Set an posterior to a file

1	set_posterior(file, sti, ai, pi, posterior)

`file`	A loaded parameter file
`sti`	the species tree index, a value from 1 to and including 2
`ai`	the alignment index, the ai-th alignment of that species tree, a value from 1 to and including the number of alignments per species tree
`pi`	the posterior index, the pi-th posterior of that alignment, a value from 1 to and including the number of posteriors per alignment
`posterior`	a posterior, may also be NA