How to make **hello** produce hello in italics?

Question

I know I can make *hello* produce hello in bold typeface. But how would I, in addition, make **hello** produce hello in italics?

\documentclass{article}

\begingroup\lccode`\~=`* \lowercase{\endgroup\def~#1~}{{\bfseries #1}}
\catcode`*=13

\begin{document}
*this is bold typeface*                 % works
**this should be italic typeface**      % how to do this?
\end{document}