hard coded HDPI column in summary

[ThomasKraft]

In the line referenced below, the column name in output table for summarize_srm_results and therefore summarize_strand_results is hardcoded to correspond to the default HDPI of 0.90. This can be confusing for users because changing the argument does not change the table header, even though the numbers within do properly shift.

https://github.com/ctross/STRAND/blob/943f37bf8191cbf4bce9eb0aad95a6575652fcf3/R/summarize_srm_results.R#L153

Easy fix is to replace with: colnames(df) = c("Variable", "Median", paste("HDPI", (1-HDPI)/2, sep=":"), paste("HDPI", (1+HDPI)/2, sep=":"), "Mean","SD")