Begins attempts to keep track of display metrics.

i.e. a system that can both make smart decisions about when to use a lower resolution, and hopefully allow some sort of flywheel-esque horizontal retrace synchronisation. And possibly some raster beam chasing?

Outputs/DisplayMetrics.cpp

@@ -0,0 +1,20 @@
+//
+//  DisplayMetrics.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 04/03/2019.
+//  Copyright © 2019 Thomas Harte. All rights reserved.
+//
+
+#include "DisplayMetrics.hpp"
+
+using namespace Outputs::Display;
+
+void Metrics::announce_event(ScanTarget::Event event) {
+}
+
+void Metrics::announce_did_resize() {
+}
+
+void Metrics::announce_draw_status(size_t lines, std::chrono::high_resolution_clock::duration duration, bool complete) {
+}