Src. Add parsing and printing of numbered item lists.

Src. Add parsing and printing of numbered item lists.

Add a member *number* to *Conf* struct, which is a printing template
for the case of numbered list. In *winnow*, identify number patterns,
store it them as template in *conf* and remove it. In *output* print
according to pattern. Also provide some basic tests.

A special treatment is in printing is that number width is adopted to
the length for right alignment. A special treatment in parsing is that
the widest numbered list item should be used for pattern definition.
Only for that you can tell about leading and trailing spaces.

TODO Clean up (refactor) number pattern parsing in *winnow*.

TODO Write some useful instructions in *README* from above commit
     message.