Pomelo: graphical forth shell (#261)

This PR adds a graphical forth shell to pomelo, simulating the
experience of an actual device. The previous terminal shell is available
in parallel.

---------

Co-authored-by: Anatol Ulrich <e+github@mail.taugt.net>
Co-authored-by: Eliza Weisman <eliza@buoyant.io>

platforms/melpomene/src/sim_drivers/emb_display.rs

@@ -293,6 +293,8 @@ async fn render_loop(
  }
 }
 
+// TODO: move to shared helper module - https://github.com/tosc-rs/mnemos/issues/260
+// TODO: blocked on e-g update https://github.com/tosc-rs/mnemos/issues/259
 fn draw_to(dest: &mut HeapArray<u8>, src: &MonoChunk, width: u32, height: u32) {
  let meta = src.meta();
  let data = src.data();
@@ -347,6 +349,9 @@ fn draw_to(dest: &mut HeapArray<u8>, src: &MonoChunk, width: u32, height: u32) {
  }
 }
 
+// TODO: move to shared helper module - https://github.com/tosc-rs/mnemos/issues/260
+// TODO: blocked on e-g update https://github.com/tosc-rs/mnemos/issues/259
+
 /// Create and return a Simulator display object from raw pixel data.
 ///
 /// Pixel data is turned into a raw image, and then drawn onto a SimulatorDisplay object