* Debug mode: no longer enables the DebugOverlay (F3) by default, but
does now insert the current FPS counter into the window title bar.
* ui.Frame: set a default "mostly transparent" BG color so the frame
background doesn't render as white.
* Add the MenuScene which will house the game's main menus.
* The "New Level" menu is first to be added.
* UI lets you pick Page Type and Wallpaper using radio buttons.
* Page Type: Unbounded, Bounded (default), No Negative Space, Bordered
* Fix bugs in uix.Canvas to fully support all these page types.
* On the Doodads tab is the Link button to enter the Link Tool.
* Click Link, then click the 1st doodad on the level, then click the 2nd
doodad to complete the link.
* The actors struct in the Level holds the link IDs for each actor.
* Build the app with -tags="shareware" to compile the free/shareware
build of the game.
* `make build-free` compiles both binaries to the bin/ folder in
shareware mode.
* The constant balance.FreeVersion is true in the shareware build and
all functionality related to the Doodad Editor UI mode is disabled
in this build mode.
The "Save As" and "Open" buttons still used an old implementation that
assumed you were talking about files only in the "./maps" folder instead
of loading them from the user's levels and doodads folders.
Now all of the menu buttons in Edit Mode intelligently open files the
same as the `edit <filename>` command from the dev console. You can omit
the file extension and it will attempt to load a Level before a Doodad
to find the first named file, or provide the full extension to be
specific.
* Scenes can insert custom key/value labels to the debug overlay and
track string variables in real time
* Added ability to unthrottle FPS in main loop
