Added cdf and quantiles for normal and chi-squared distribution

Meta-analyses and many other workflows make use of the cumulative and inverse cumulative distribution functions for the standard normal distribution and chi-squared distribution with 1 degree of freedom. So we’ve added efficient implementations of these fundamental functions to the expression language: see the new Statistics section in the expression language function docs for details on pnorm, qnorm, pchisq1tail and qchisq1tail.

The functions pchisq1tail(x) and qchisq1tail(p) have been replaced by the more general functions pchisqtail(x,df) and qchisqtail(p,df), where df is the number of degrees of freedom.