Adds just enough logic to make every host key look like '0' to the MSX.

Machines/MSX/Keyboard.cpp

@@ -0,0 +1,14 @@
+//
+//  Keyboard.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/11/2017.
+//  Copyright © 2017 Thomas Harte. All rights reserved.
+//
+
+#include "Keyboard.hpp"
+
+uint16_t MSX::KeyboardMapper::mapped_key_for_key(Inputs::Keyboard::Key key) {
+	// TODO: actual keyboard map.
+	return 0;
+}