pseudo-mousing during pause

Some terminals use the same window for text entry and graphical display, including terminal types dumb, sixel, kitty, and domterm. These terminals do not currently support mousing per se, but during a pause mouse command they interpret keystrokes in the same way that a mousing terminal would. I.e. l toggles log-scale axes, a autoscales the current plot, left/right/up/down arrow keys change the view angle of 3D plots and perform incremental pan/zoom steps for 2D plots. h displays a list of key bindings. A carriage return terminates the pause and restores normal command line processing.