Add solutions for part 1

tools/builtInChips/FullAdder.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/FullAdder.hdl
+
+/**
+ * Full adder. Computes sum, the least significant bit of 
+ * a + b + c, and carry, the most significant bit of a + b + c.
+ */
+
+CHIP FullAdder {
+
+    IN  a, b, c;
+    OUT sum,     // LSB of a + b + c
+        carry;   // MSB of a + b + c
+
+    BUILTIN FullAdder;
+}
+