Update multi new method

1. Add new method in ALU to covert between string and singed value.
2. Add new method in ALU to check overflow.
3. Add new method in Register to set specific bit of any register.
4. Check and modified the method implemented in phase one.
update new method

1. Add new method in ALU to covert between string and singed value.
2. Add new method in ALU to check overflow.
3. Add new method in Register to set specific bit of any register.
4. Check and modified the method implemented in phase one.