Add Discord RPC (#161)

* Add discord-rpc submodule

* Add Discord RPC

* Fix up Discord status

* Fix CMake because MacOS sucks

* Slightly less hacky fix

src/discord_rpc.cpp

@@ -0,0 +1,41 @@
+#ifdef PANDA3DS_ENABLE_DISCORD_RPC
+
+#include "discord_rpc.hpp"
+
+#include <cstring>
+#include <ctime>
+
+void Discord::RPC::init() {
+	DiscordEventHandlers handlers{};
+	Discord_Initialize("1138176975865909360", &handlers, 1, nullptr);
+
+	startTimestamp = time(nullptr);
+	enabled = true;
+}
+
+void Discord::RPC::update(Discord::RPCStatus status, const std::string& game) {
+	DiscordRichPresence rpc{};
+
+	if (status == Discord::RPCStatus::Playing) {
+		rpc.details = "Playing a game";
+		rpc.state = game.c_str();
+	} else {
+		rpc.details = "Idle";
+	}
+
+	rpc.largeImageKey = "pand";
+	rpc.largeImageText = "Panda3DS is a 3DS emulator for Windows, MacOS and Linux";
+	rpc.startTimestamp = startTimestamp;
+
+	Discord_UpdatePresence(&rpc);
+}
+
+void Discord::RPC::stop() {
+	if (enabled) {
+		enabled = false;
+		Discord_ClearPresence();
+		Discord_Shutdown();
+	}
+}
+
+#endif