Rework example code, fix bugs and get to compiling state. Also introduce missing logic for the Matrix code to keep track of what column is active.

Matrix.h

@@ -0,0 +1,24 @@
+// A state-keeping class used with MatrixReader. Keeps track of which column is active,
+// switches between them.
+
+#ifndef _MATRIX_H_
+#define _MATRIX_H_
+
+#include <Arduino.h>
+
+class Matrix {
+ public:
+  Matrix(uint8_t *columns, bool inverted=true);
+  void Activate(uint8_t column);
+
+ private:
+  void _enable(uint8_t pin);
+  void _disable(uint8_t pin);
+  
+  uint8_t* columns;
+  uint8_t active_pin;
+  uint8_t num_columns;
+  bool inverted;
+};
+
+#endif