Allow variables to be broken across pages

The previous implementation assumed you would never want a factor variable to be broken over two pages.  This creates problems if you are using a factor that has more levels than max.rows.  Specifically, if you make a table of one variable or a table where the first variable has more levels than max.rows, if you try to keep the variable together, there will be no data to display on the first page.  split_ctable doesn't like this very much.  Setting keepVarTogether=FALSE forces exactly max.rows displayed on each page (except maybe the last)