Add versionadded for operator.pow

Doc/lib/liboperator.tex

@@ -134,6 +134,7 @@ Return \var{o} positive.
 \begin{funcdesc}{pow}{a, b}
 \funcline{__pow__}{a, b}
 Return \var{a} \code{**} \var{b}, for \var{a} and \var{b} numbers.
+\versionadded{2.3}
 \end{funcdesc}
 
 \begin{funcdesc}{rshift}{a, b}