This PR makes a couple of small improvements to the calculation of window widths when the ratios option is applied:

• Previously space would not be set aside for dividers when calculating window widths, and instead each window would just leave its final column blank to simulate a divider when drawing the UI. Now the space for dividers is allocated properly and does not form part of the window dimensions.
• Window widths are floored if they are not whole numbers, and the discarded fractional parts are accumulated and added only to the rightmost window, which can cause it to be larger than expected. Now the discarded fractional parts will be added to each successive window where possible, so that it is spread out and not added to just one window at the end.