Add solutions for part 1

tools/builtInChips/PC.hdl

@@ -0,0 +1,22 @@
+// 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/PC.hdl
+
+/**
+ * 16-bit counter with load and reset controls.
+ *
+ * If reset(t-1) then out(t) = 0
+ *    else if load(t-1) then out(t) = in(t-1)
+ *         else if inc(t-1) then out(t) = out(t-1) + 1 (integer addition)
+ *              else out(t) = out(t-1)
+ */
+
+CHIP PC {
+
+    IN  in[16], load, inc, reset;
+    OUT out[16];
+
+    BUILTIN PC;
+    CLOCKED in, load, inc, reset;
+}