Add README

README.md

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+# catbox
+
+Work in progress game engine, inspired by [arcade](arcade.academy/).
+
+```rs
+use catbox::{Event, Game, Keycode, Sprite};
+
+fn main() {
+    let game = Game::new("catbox demo", 1000, 800);
+
+    let mut i = 0.0;
+    let mut s = Sprite::new("duck.png", 500, 400).unwrap();
+    game.run(|canvas, event_pump| {
+        i = (i + 1.0) % 360.0;
+
+        let (start_x, start_y) = s.position();
+        let m = sdl2::mouse::MouseState::new(event_pump.as_ref());
+        let x_diff = m.x() - start_x;
+        let y_diff = m.y() - start_y;
+
+        let angle = (y_diff as f64).atan2(x_diff as f64);
+        s.set_angle(angle.to_degrees());
+
+        for event in event_pump {
+            match event {
+                Event::Quit { .. }
+                | Event::KeyDown {
+                    keycode: Some(Keycode::Escape),
+                    ..
+                } => game.terminate(),
+
+                Event::KeyDown { keycode, .. } => {
+                    let offset = match keycode.unwrap() {
+                        Keycode::W | Keycode::Up => (0, 5),
+                        Keycode::S | Keycode::Down => (0, -5),
+                        Keycode::A | Keycode::Left => (5, 0),
+                        Keycode::D | Keycode::Right => (-5, 0),
+                        _ => (0, 0),
+                    };
+
+                    s.translate(offset);
+                }
+                _ => {}
+            }
+        }
+
+        s.draw(canvas).unwrap();
+    })
+    .unwrap();
+}
+```