gui_toolkit 0.71.0

Added

• Docking (ui/dock_model.odin, ui/docking.odin, docs/docking.md): the app's panels in stacks of tabs the user rearranges. The layout is the app's ui.Dock, flat data: a tree of nodes in one #soa array (leaves: a stack of panels and the one shown; splits: an axis, a ratio, the second side folded), floating roots at a place of their own, the panels (the app's u32 ids) in tab order; dock_add, dock_move (into a stack at a tab, at a side of one, at an edge of the space, floating), dock_move_node, dock_redock, dock_close, dock_activate, dock_set_split, dock_layout, dock_target_at; one line of text (dock_format / dock_parse: unknown names dropped with the stacks they leave empty, the panels it does not name placed by the app, any other text refused with the dock left as it was). dock_begin / dock_panel / dock_end build it: a tab dragged out shows the drop targets (five squares over the stack under the pointer, four at the edges of the space, the strips between their tabs) and a translucent preview of where it lands; let go elsewhere it floats (an overlay of the window with a frame and a shadow, moved by its strip with the drop targets, resized by its corner, docked back by a double click); Escape cancels; the handles are pane_split's (minimum sizes, fold); close buttons, a middle click; the stack's menu reaches every drop target from the keyboard; the arrows along a strip, Ctrl+Shift+arrows move a tab, Ctrl+Tab goes through a stack; roles tab list, tab (controls its panel), tab panel, separator. Theme entries dock_preview and dock_marker. Example examples/docking; tests tests/docking (the model and the text; the drags, the keyboard and the menu through the test session).