Add the ai files that were forgotten in previous commit

src/ai.c

@@ -0,0 +1,10 @@
+#include "ai.h"
+#include "engine.h"
+
+const char moves[] = {'w', 'a', 's', 'd'};
+
+int ai_move(struct gamestate *g)
+{
+    if (g->opts->interactive) usleep(50000);
+    return moves[rand() % 4];
+}