One major weekend coding session later...

I hate doing this as one giant commit, but I was under the gun and had
to just code as fast as I could, so some common software development
things had to be skipped. Mostly git commits.

Here we have several mini applications that reside on the microbit.
* Menu - The main app switching presentation.
* Badge - A name scroller.
* Snake - A snake game.

The switcher task is the main running task of the program. All the logic
goes through here. It will pass the running off to different apps. When
an app returns from its main function it will return the next app to
switch to.

The display task is a PWM LED matrix updater. It will turn on the LEDs
for what ever frame is passed to it. It keeps a backing frame for draw
calls that occur between new frames arriving.

There are several button listeners for input handling.

Everything is sent using channels, button input and presentation frames.

src/menu.rs

@@ -0,0 +1,4 @@
+mod menu;
+mod renderer;
+
+pub use crate::menu::menu::Menu;