Added support for Segmentedlist.

Added support for Segmentedlist.
Details: Output is tabular, with no option for "list" type output.
Output for Segtitle elements can be supressed by setting
man.segtitle.suppress. If Segtitle content is output, it is
rendered in italic type (not bold because not all terminals
support bold and so italic ensures the stand out on those
terminals). Extra space (.sp line) at end of table code ensures
that it gets handled correctly in the case where its source is the
child of a Para.  Closes feature-request #1400097. Thanks to
Daniel Leidert for the patch and push, and to Alastair Rankine for
filing the original feature request.