Add "Snake" game example

examples/game/01-snake/snake.h

@@ -0,0 +1,51 @@
+/*
+ * Interface definition of the Snake game.
+ *
+ * This code is public domain. Feel free to use it for any purpose!
+ */
+#ifndef SNAKE_H
+#define SNAKE_H
+#define SNAKE_GAME_WIDTH  24U
+#define SNAKE_GAME_HEIGHT 18U
+#define SNAKE_MATRIX_SIZE (SNAKE_GAME_WIDTH * SNAKE_GAME_HEIGHT)
+
+typedef enum
+{
+    SNAKE_CELL_NOTHING = 0U,
+    SNAKE_CELL_SRIGHT = 1U,
+    SNAKE_CELL_SUP = 2U,
+    SNAKE_CELL_SLEFT = 3U,
+    SNAKE_CELL_SDOWN = 4U,
+    SNAKE_CELL_FOOD = 5U
+} SnakeCell;
+
+#define SNAKE_CELL_MAX_BITS 3U /* floor(log2(SNAKE_CELL_FOOD)) + 1 */
+
+typedef enum
+{
+    SNAKE_DIR_RIGHT,
+    SNAKE_DIR_UP,
+    SNAKE_DIR_LEFT,
+    SNAKE_DIR_DOWN
+} SnakeDirection;
+
+typedef struct
+{
+    unsigned char cells[(SNAKE_MATRIX_SIZE * SNAKE_CELL_MAX_BITS) / 8U];
+    char head_xpos;
+    char head_ypos;
+    char tail_xpos;
+    char tail_ypos;
+    char next_dir;
+    char inhibit_tail_step;
+    unsigned occupied_cells;
+} SnakeContext;
+
+typedef int (*RandFunc)(int n);
+
+void snake_initialize(SnakeContext *ctx, RandFunc rand);
+void snake_redir(SnakeContext *ctx, SnakeDirection dir);
+void snake_step(SnakeContext *ctx, RandFunc rand);
+SnakeCell snake_cell_at(const SnakeContext *ctx, char x, char y);
+
+#endif /* SNAKE_H */