Fixed docs, changed "g:votl_" to "g:vo_".
Added "g:vo_fold_length", for customisation.

Options are either a number, which will be the length (not trimmed, only
affecting dashes) of the fold column, or "max", which will make the
dashes fill the column.

Set in .vimoutlinerrc, like

let g:vo_fold_length="max"