Wide-mode for viewing panel

I find that when using HackMD for sequence diagrams, and other visual artifacts, the max-width in the viewing panel can make reading horizontally packed diagrams very difficult. In looking at the CSS, I found that simply removing the `max-width` set on the `#doc` element expands the readable area and allows diagrams to scale up to sizes that are easier to read. Would you consider adding a UI toggle switch that allowed users to toggle to a wide-mode view setting?