Implement Project 2: Arithmetic Logic Unit

✅ HalfAdder: XOR for sum, AND for carry
✅ FullAdder: Two half adders + OR
✅ Add16: Chain of 16 full adders with carry
✅ Inc16: Add16 with constant 1
✅ ALU: Complete arithmetic logic unit with all operations

Used concise, student-style comments throughout.

02/HalfAdder.hdl

@@ -7,9 +7,11 @@
  */
 CHIP HalfAdder {
     IN a, b;    // 1-bit inputs
-    OUT sum,    // Right bit of a + b 
+    OUT sum,    // Right bit of a + b
         carry;  // Left bit of a + b
 
     PARTS:
-    //// Replace this comment with your code.
+    // sum = a XOR b, carry = a AND b
+    Xor(a=a, b=b, out=sum);
+    And(a=a, b=b, out=carry);
 }