Add solutions for part 1

tools/builtInChips/DMux4Way.hdl

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+// 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/DMux4Way.hdl
+
+/**
+ * 4-way demultiplexor.  
+ * {a,b,c,d} = {in,0,0,0} if sel == 00
+ *             {0,in,0,0} if sel == 01
+ *             {0,0,in,0} if sel == 10
+ *             {0,0,0,in} if sel == 11
+ */
+
+
+CHIP DMux4Way {
+
+    IN  in, sel[2];
+    OUT a, b, c, d;
+
+    BUILTIN DMux4Way;
+}
+