Add toggle_auto_zoom key binding, defaulting to Z

Closes #218

man/feh.pre

@@ -1376,6 +1376,10 @@ Close current window
 .
 Jump to a random position in the current filelist
 .
+.It Z Bq toggle_auto_zoom
+.
+Toggle auto-zoom.
+.
 .It \&[, \&] Bq prev_dir, next_dir
 .
 Jump to the first image of the previous or next sequence of images sharing

src/keyevents.c

@@ -185,6 +185,7 @@ void init_keyevents(void) {
 	feh_set_kb("render"    , 0, XK_KP_Begin  , 0, XK_R         , 0, 0);
 	feh_set_kb("toggle_actions" , 0, XK_a, 0, 0, 0, 0);
 	feh_set_kb("toggle_aliasing" , 0, XK_A, 0, 0, 0, 0);
+	feh_set_kb("toggle_auto_zoom" , 0, XK_Z, 0, 0, 0, 0);
 #ifdef HAVE_LIBEXIF
 	feh_set_kb("toggle_exif" , 0, XK_e, 0, 0, 0, 0);
 #endif
@@ -637,6 +638,10 @@ void feh_event_handle_generic(winwidget winwid, unsigned int state, KeySym keysy
 		winwid->force_aliasing = !winwid->force_aliasing;
 		winwidget_render_image(winwid, 0, 0);
 	}
+	else if (feh_is_kp(EVENT_toggle_auto_zoom, state, keysym, button)) {
+		opt.zoom_mode = (opt.zoom_mode == 0 ? ZOOM_MODE_MAX : 0);
+		winwidget_rerender_all(1);
+	}
 	else if (feh_is_kp(EVENT_toggle_filenames, state, keysym, button)) {
 		opt.draw_filename = !opt.draw_filename;
 		winwidget_rerender_all(0);

src/options.h

@@ -189,6 +189,7 @@ enum key_action {
 	EVENT_render,
 	EVENT_toggle_actions,
 	EVENT_toggle_aliasing,
+	EVENT_toggle_auto_zoom,
 #ifdef HAVE_LIBEXIF
 	EVENT_toggle_exif,
 #endif