1. Add Easy Difficulty. This difficulty has 5 lives at the beginning. The weapon is retained after the character dies. 50 kills will reward one life. Other aspects are the same as the Normal Difficulty.
2. Changed "Press any key" to "Hold any key" for 2 seconds
1. 增加 简单难度 ，这个难度初始有5生命，角色死亡后武器保留，50击杀奖励一命，其他方面和普通难度一致
2. “按任意键跳过” 改为 “按住任意键跳过”2秒