前面output都對的版本
如果對照cache的output，在cycle 97(發生readmiss，要第二次writeback)時開始錯
不過我也沒辦法保證前面的cycle沒問題(register那邊的output，我沒有對照)

mainly change about PC
add stall signal to PC
fix a bug of previous project -- the connection between Hazard_Detection & PC (no matter)