upstream_polymerase_ratio: density ratio calculation
In ndukler/tuSelecter2: Selecting transcript model using PRO-seq

Calculates the log2 ratio of the polymerase upstream and downstream of the TSS on the sense strand. This ratio is used to determine if a transcript may be active. Used during data addition to determine if a transcript specified as inactive in the fit call should be overriden.NOTE: ratio is calculated with an additional 1 pseudocount/kb added to the numerator and denominator

upstream_polymerase_ratio(
  tq,
  bigwig_plus,
  bigwig_minus,
  up_width = 5000,
  up_shift = 500,
  body_width = 5000,
  body_shift = 500
)

`tq`	A transcript_quantifier-class object
`bigwig_plus`	the path to a bigwig for reads on the plus strand
`bigwig_minus`	the path to a bigwig for reads on the minus strand
`up_width`	The length of the region upstream of the TSS to calculate the polymerase denisty in
`up_shift`	how far upstream of the TSS `up_width` is shifted
`body_width`	The length of the region downstream of the TSS to calculate the polymerase denisty in
`body_shift`	how far downstream of the TSS `body_width` is shifted