Important Change

1. Stop using alu_top in ALU. Use simpler(?) implementation.
2. Support MUL and use 3'b010 to indicate R-Type inst.
3. Support JUMP. Update ALU_op to match the codec in ALU_Ctrl.
4. Add Mux for Jump
5. Update TestBench to Lab3
Add File

1. Data_Memory
2. MUX_4to1