gui_toolkit 0.68.0

Added

• ui.pane_split, ui.pane_toggle, ui.Pane: panes the user resizes from a few em (PANE_MIN_EM) to all the room but a few em for the other side, folds (a drag under half the minimum, a double click, Enter, a chevron button) to a strip that brings them back (a click, Enter, a pull), and places at the side or below (pane_axis, pane_place_menu); the app owns a Pane per split (sizes per orientation, folded, place) and saves it through Pane_Options.on_save; pane_format / pane_parse make it a line of text; menu_move_to lists "Move to" items for a tab that may go to another strip. Keyboard (arrows, Home, End, Enter) and accessible (a separator with its value, expanded). examples/panes uses them. Tests tests/panes/pane_split_test.odin