feat: add XDG autostart support for automatic application launching

feat: implement demo mode for automated feature showcase
feat: add XEmbed system tray protocol for external application icons
feat: add window snapping to left and right halves
feat: add minimize/restore toggle with Alt+F9 keybinding
docs: update README with new features and configuration details
build: update build system for new autostart and demo modules

build/workspace.d

@@ -1,6 +1,6 @@
 build/workspace.o: src/workspace.c include/workspace.h include/dwn.h \
  include/client.h include/layout.h include/atoms.h include/util.h \
- include/config.h
+ include/config.h include/panel.h
 include/workspace.h:
 include/dwn.h:
 include/client.h:
@@ -8,3 +8,4 @@ include/layout.h:
 include/atoms.h:
 include/util.h:
 include/config.h:
+include/panel.h: