Attempts to get as far as running the MultiMachine.

In doing so, fixes the long-standing bug that machines that output audio but don't have a listener produce a divide by zero.

Analyser/Dynamic/MultiMachine/Implementation/MultiCRTMachine.cpp

@@ -0,0 +1,70 @@
+//
+//  MultiCRTMachine.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/01/2018.
+//  Copyright © 2018 Thomas Harte. All rights reserved.
+//
+
+#include "MultiCRTMachine.hpp"
+
+using namespace Analyser::Dynamic;
+
+MultiCRTMachine::MultiCRTMachine(const std::vector<std::unique_ptr<::Machine::DynamicMachine>> &machines) :
+	machines_(machines) {}
+
+void MultiCRTMachine::setup_output(float aspect_ratio) {
+	for(const auto &machine: machines_) {
+		CRTMachine::Machine *crt_machine = machine->crt_machine();
+		if(crt_machine) crt_machine->setup_output(aspect_ratio);
+	}
+}
+
+void MultiCRTMachine::close_output() {
+	for(const auto &machine: machines_) {
+		CRTMachine::Machine *crt_machine = machine->crt_machine();
+		if(crt_machine) crt_machine->close_output();
+	}
+}
+
+Outputs::CRT::CRT *MultiCRTMachine::get_crt() {
+	CRTMachine::Machine *crt_machine = machines_.front()->crt_machine();
+	return crt_machine ? crt_machine->get_crt() : nullptr;
+}
+
+Outputs::Speaker::Speaker *MultiCRTMachine::get_speaker() {
+	CRTMachine::Machine *crt_machine = machines_.front()->crt_machine();
+	return crt_machine ? crt_machine->get_speaker() : nullptr;
+}
+
+void MultiCRTMachine::run_for(const Cycles cycles) {
+	for(const auto &machine: machines_) {
+		CRTMachine::Machine *crt_machine = machine->crt_machine();
+		if(crt_machine) crt_machine->run_for(cycles);
+	}
+
+	// TODO: announce an opportunity potentially to reorder the list of machines.
+}
+
+double MultiCRTMachine::get_clock_rate() {
+	// TODO: something smarter than this? Not all clock rates will necessarily be the same.
+	CRTMachine::Machine *crt_machine = machines_.front()->crt_machine();
+	return crt_machine ? crt_machine->get_clock_rate() : 0.0;
+}
+
+bool MultiCRTMachine::get_clock_is_unlimited() {
+	CRTMachine::Machine *crt_machine = machines_.front()->crt_machine();
+	return crt_machine ? crt_machine->get_clock_is_unlimited() : false;
+}
+
+void MultiCRTMachine::set_delegate(::CRTMachine::Machine::Delegate *delegate) {
+	// TODO
+}
+
+void MultiCRTMachine::machine_did_change_clock_rate(Machine *machine) {
+	// TODO
+}
+
+void MultiCRTMachine::machine_did_change_clock_is_unlimited(Machine *machine) {
+	// TODO
+}