Improve spanned table creation

[zhiburt]

I accidentally bumped into wiki and noticed this.

It's must be possible to do with tabled already. (Maybe the layout would be a bit different, which is actually also a subject for improvements ref #274) But it would require many Span calls.

table.with(Span::new())

I wonder could we simplify the interface to build it? Maybe some macros?

If anyone has any thoughts how it could look like would be interesting to hear.