queue: Implement a more flexible event queue

test/unit/fixtures/queue.c

@@ -0,0 +1,16 @@
+#include <string.h>
+#include <stdlib.h>
+#include "nvim/event/queue.h"
+#include "queue.h"
+
+
+void ut_queue_put(Queue *queue, const char *str)
+{
+  queue_put(queue, NULL, 1, str);
+}
+
+const char *ut_queue_get(Queue *queue)
+{
+  Event event = queue_get(queue);
+  return event.argv[0];
+}