sample: ch08: signal1.c -> sample/ch08/signal1.c
sample: ch08: signal1.c: 调整编码风格
sample: ch08: signal1.c: 增加说明性注释
sample: ch08: signal2.c -> sample/ch08/signal2.c
sample: ch08: signal2.c: 更改编码风格
sample: ch08: signal2.c: 增加说明性注释
sample: ch08: signal3.c -> sample/ch08/signal3.c
sample: ch08: signal3.c: 调整编码风格
sample: ch08: signal3.c: 增加说明性注释
exercise: 8.8
exercise: 8.8: 调整编码风格