Columns calculation in MenuSupport is unreliable

[tpoliaw]

If Option.LIST_ROW_FIRST and Option.MENU_COMPLETE are both set for a LineReader, the number of columns can be calculated incorrectly in the MenuSupport instance.

In the case I've found, I have 9 completion candidates and it's splitting them onto two rows with 6 and 3 options respectively. The columns calculation assumes the minimum number of columns are used for the number of lines (giving 5 columns).

I'm not sure if the best way to handle it, either forcing the minimum number of columns without increasing the number of rows, or to return the number of columns somehow.

Let me know which you'd prefer and I'm happy to work on a PR. I have another couple in that area that I'd like to submit soonish as well.

[gnodet]

I think forcing the minimum number of columns without increasing the number of rows would be the best looking option, but I don't have a strong opinion.

[tpoliaw]

I'm still not sure either way, but if you want to minimise the number of columns, I think #196 should fix it.