Include estimate of probability within RoPE when plotting

[arc12]

In cases such as az.plot_posterior(inference_data, rope=(0.45, 0.55)), it would be useful to include an estimate of the probability within the rope. (as an option, I suspect)

For Kruschke's version, see: http://doingbayesiandataanalysis.blogspot.com/2013/08/how-much-of-bayesian-posterior.html

we could extent this idea, in a similar way to how ref_val works to show probabilities for the Rope and both upper and lower tails.

[Rishabh261998]

Can I take this issue? Thank You
Idea: Just use the end-points of the rope as 2 ref_val and use them to get the probability within the rope