Add vis after fixing some inconveniences found in my last attempt 
<http://lists.gnu.org/archive/html/guix-devel/2016-12/msg00068.html>. I 
can't run guix lint on it now, but I haven't changed anything too 
important, so it should be fine.

This package requires libtermkey and lua-lpeg, for which I submitted two 
patches (see my last two messages). Be sure to add them before.

José Miguel Sánchez García