* New doodads: Switches.
* They come in four varieties: wall switch (background element, with
"ON/OFF" text) and three side-profile switches for the floor, left
or right walls.
* On collision with the player, they flip their state from "OFF" to
"ON" or vice versa. If the player walks away and then collides
again, the switch flips again.
* Can be used to open/close Electric Doors when turned on/off. Their
default state is "off"
* If a switch receives a power signal from another linked switch, it
sets its own state to match. So, two "on/off" switches that are
connected to a door AND to each other will both flip on/off when one
of them flips.
* Update the Level Collision logic to support Decoration, Fire and Water
pixel collisions.
* Previously, ALL pixels in the level were acting as though solid.
* Non-solid pixels don't count for collision detection, but their
attributes (fire and water) are collected and returned.
* Updated the MenuScene to support loading a map file in Play Mode
instead of Edit Mode. Updated the title screen menu to add a button
for playing levels instead of editing them.
* Wrote some documentation.
The `level.Canvas` is a widget that holds onto its Palette and Grid and
has interactions to allow scrolling and editing the grid using the
swatches available on the palette.
Thus all of the logic in the Editor Mode for drawing directly onto the
root SDL surface are now handled inside a level.Canvas instance.
The `level.Canvas` widget has the following properties:
* Like any widget it has an X,Y position and a width/height.
* It has a Scroll position to control which slice of its drawing will be
visible inside its bounding box.
* It supports levels having negative coordinates for their pixels. It
doesn't care. The default Scroll position is (0,0) at the top left
corner of the widget but you can scroll into the negatives and see the
negative pixels.
* Keyboard keys will scroll the viewport inside the canvas.
* The canvas draws only the pixels that are visible inside its bounding
box.
This feature will eventually pave the way toward:
* Doodads being dropped on top of your map, each Doodad being its own
Canvas widget.
* Using drawings as button icons for the user interface, as the Canvas
is a normal widget.
