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/systray.d

@@ -17,7 +17,7 @@ build/systray.o: src/systray.c include/systray.h include/dwn.h \
  /usr/include/dbus-1.0/dbus/dbus-server.h \
  /usr/include/dbus-1.0/dbus/dbus-signature.h \
  /usr/include/dbus-1.0/dbus/dbus-syntax.h \
- /usr/include/dbus-1.0/dbus/dbus-threads.h
+ /usr/include/dbus-1.0/dbus/dbus-threads.h include/atoms.h
 include/systray.h:
 include/dwn.h:
 include/panel.h:
@@ -42,3 +42,4 @@ include/notifications.h:
 /usr/include/dbus-1.0/dbus/dbus-signature.h:
 /usr/include/dbus-1.0/dbus/dbus-syntax.h:
 /usr/include/dbus-1.0/dbus/dbus-threads.h:
+include/atoms.h: