Hide left-hand sidebar

The left-hand sidebar (with the Sessions and Requests menus) takes up valuable screen width all the time even though I never use it.  I can't make it narrower than a certain minimum width and the only way I can hide it completely is to move the whole window partially off screen, which also hides the window controls at the top left.

It would be great to have a way to hide it completely.  Some people might want to be able to toggle it easily.