Plot top and bottom bins for the monthly frequency plot

Is there any appetite for adding functionality to plot the "top" and "bottom" bins associated with the monthly frequency plots (0-5th percentile and 95-100th percentile)?

Primary benefit is explicit visualization of minimum and maximum values that have been measured for a given site in a given month.

Happy to contribute to this change but wanted to ask before trying to code it up - let me know @ldecicco