Cosmic Unicorn version!

This is just a bit of fun, so not really planning to merge into RP2040 branch. Note the unicorn version (without rewriting all the drawing completely) adds quite a bit of code, so this only builds with Clang

To build with Clang, you need >1.5.0/develop of pico-sdk (and pico_extras), and pass -DPICO_COMPILER=pico_arm_clang, and -DPICO_TOOLCHAIN_PATH=path to ARM embedded LLVM 14.0.0 to CMake.

You must also specify -DPICO_BOARD=pimoroni_cosmic_unicorn to CMake also (or in your env). You want to build doom_tiny_unicorn (the others won't work)

Note that the unicorn uses 16K of RAM for the frame buffer, and so that is new RAM we didn't have space for, so i have decreased the size of the columns area. You may experience OOM on some levels, or visual distortion

Here are the keys:

   Sleep: Enter / Fire (keyboard L-CTRL & Return)
   Vol+: UP/Forward (keyboard Up)
   Vol-: Down/Backward (keyboard Down)
   Brightness+: Back one menu (keyboard Backspace)
   Brightness-: Toggle menu (keyboard Escape)
   A: Right (keyboard Right)
   B: Left (keyboard Left)
   C: Door open (keyboard Space)
   D: Strafe (keyboard Alt)
   
   You can start a game with Enter/Enter/Enter