Add prev_dir and next_dir navigation actions

Many image collections are organized by directory, so it is nice to have
jump-to-adjacent-directory navigation.

e.g. Given the following file hierarchy:

    .
    ├── A
    │   ├── 1.jpg
    │   ├── 2.jpg
    │   └── C
    │       ├── 1.jpg
    │       ├── 2.jpg
    │       └── 3.jpg
    └── B
        ├── 1.jpg
        ├── 2.jpg
        └── 3.jpg

`feh --recursive` creates the following filelist:

    A/1.jpg <---- current_file
    A/2.jpg
    A/C/1.jpg
    A/C/2.jpg
    A/C/3.jpg
    B/1.jpg
    B/2.jpg
    B/3.jpg

If we press [next_dir], we move the current_file pointer to:

    A/1.jpg
    A/2.jpg
    A/C/1.jpg <-- current_file
    A/C/2.jpg
    A/C/3.jpg
    B/1.jpg
    B/2.jpg
    B/3.jpg

Pressing [next_dir] again moves the pointer to:

    A/1.jpg
    A/2.jpg
    A/C/1.jpg
    A/C/2.jpg
    A/C/3.jpg
    B/1.jpg <---- current_file
    B/2.jpg
    B/3.jpg

[next_dir] now moves the pointer back to the top of the list:

    A/1.jpg <---- current_file
    A/2.jpg
    A/C/1.jpg
    A/C/2.jpg
    A/C/3.jpg
    B/1.jpg
    B/2.jpg
    B/3.jpg

Pressing [prev_dir] from here moves backwards to the first image of the
previous directory:

    A/1.jpg
    A/2.jpg
    A/C/1.jpg
    A/C/2.jpg
    A/C/3.jpg
    B/1.jpg <---- current_file
    B/2.jpg
    B/3.jpg

When starting from an position that is not the first image of a
directory, [prev_dir] moves the pointer to the first image of the
current directory.

These actions combine well with `--sort dirname` since all regular files
in a directory will be sorted before any subdirectories, avoiding a
filelist like the following:

    A/1.jpg
    A/SUBDIR/2.jpg
    A/SUBDIR/3.jpg
    A/4.jpg

With `--sort dirname` that filelist becomes:

    A/1.jpg
    A/4.jpg
    A/SUBDIR/2.jpg
    A/SUBDIR/3.jpg

1 files changed, 14 insertions, 0 deletions

diff --git a/src/keyevents.c b/src/keyevents.c
index 8977111..4837c0b 100644
--- a/src/keyevents.c
+++ b/src/keyevents.c
@@ -110,6 +110,8 @@ void init_keyevents(void) {
 	feh_set_kb(&keys.next_img  , 0, XK_Right     , 0, XK_n         , 0, XK_space);
 	feh_set_kb(&keys.jump_back , 0, XK_Page_Up   , 0, XK_KP_Page_Up, 0, 0);
 	feh_set_kb(&keys.jump_fwd  , 0, XK_Page_Down , 0, XK_KP_Page_Down,0,0);
+	feh_set_kb(&keys.prev_dir  , 0, XK_bracketleft, 0, 0           , 0, 0);
+	feh_set_kb(&keys.next_dir  , 0, XK_bracketright, 0, 0          , 0, 0);
 	feh_set_kb(&keys.jump_random,0, XK_z         , 0, 0            , 0, 0);
 	feh_set_kb(&keys.quit      , 0, XK_Escape    , 0, XK_q         , 0, 0);
 	feh_set_kb(&keys.close     , 0, XK_x         , 0, 0            , 0, 0);
@@ -222,6 +224,10 @@ void init_keyevents(void) {
 			cur_kb = &keys.jump_back;
 		else if (!strcmp(action, "jump_fwd"))
 			cur_kb = &keys.jump_fwd;
+		else if (!strcmp(action, "prev_dir"))
+			cur_kb = &keys.prev_dir;
+		else if (!strcmp(action, "next_dir"))
+			cur_kb = &keys.next_dir;
 		else if (!strcmp(action, "jump_random"))
 			cur_kb = &keys.jump_random;
 		else if (!strcmp(action, "quit"))
@@ -532,6 +538,14 @@ void feh_event_handle_keypress(XEvent * ev)
 		else if (winwid->type == WIN_TYPE_THUMBNAIL)
 			feh_thumbnail_select_next(winwid, 10);
 	}
+	else if (feh_is_kp(&keys.next_dir, keysym, state)) {
+		if (opt.slideshow)
+			slideshow_change_image(winwid, SLIDE_JUMP_NEXT_DIR, 1);
+	}
+	else if (feh_is_kp(&keys.prev_dir, keysym, state)) {
+		if (opt.slideshow)
+			slideshow_change_image(winwid, SLIDE_JUMP_PREV_DIR, 1);
+	}
 	else if (feh_is_kp(&keys.quit, keysym, state)) {
 		winwidget_destroy_all();
 	}