R.PSNORM(x,shape,location,scale,lower_tail,log_p)
x: observation
shape: the shape parameter of the distribution
location: the location parameter of the distribution
scale: the scale parameter of the distribution
lower_tail: if true (the default), the lower tail of the distribution is considered
log_p: if true, log of the probability is used
This function returns the cumulative distribution function of the skew-normal distribution.