newIntronRetention: Compute intron retention
In pachterlab/kma: KeepMeAround: Intron Retention Detection in RNA-Seq data

Create an IntronRetention object.

1 2	newIntronRetention(targetExpression, intronToUnion, groups, unique_counts = NULL, psi = TRUE)

`targetExpression`	a matrix of nothing but expression values and one column containing 'target_id's
`intronToUnion`	a table with columns (all character vectors): intron the identifier of the intron target_id the target_id of transcripts compatible with the intron gene the gene name that this intron belongs to intron_extension the actual coordinates of the intron quantified (including the region that overlaps the intronic region)
`groups`	a vector with the grouping
`psi`	if TRUE, compute the psi value. otherwise, compute a rate