Add solutions for part 1

tools/builtInChips/Xor.hdl

@@ -0,0 +1,16 @@
+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: tools/builtIn/Xor.hdl
+
+/**
+ *  Exclusive-or gate: out = !(a == b).
+ */
+
+CHIP Xor {
+
+    IN  a, b;
+    OUT out;
+
+    BUILTIN Xor;
+}