* Integrate the new ui.MenuBar into the Editor Scene.
* File: New Level/Doodad, Save [as], Open, Close, Exit
* Edit: Undo, Redo, Level options
* Level: Playtest
* Tools: Debug overlay, Command shell
* Help: User Manual, About
* Add an About dialog accessible from the Help menu.
* Update the Makefile to choose MacOS friendly `date` formats.
* Build the Windows doodle.exe binary as a GUI application to skip the
console window.
* Added Mac OS build instructions.
