Logging: Add customizable logging backends and fmtlib based macros

* Change the logging backend to support multiple sinks through the
Backend Interface
* Add a new set of logging macros to use fmtlib instead.
* Qt: Compile as GUI application on windows to make the console hidden by
default. Add filter configuration and a button to open log location.
* SDL: Migrate to the new logging macros

src/citra_qt/debugger/console.cpp

@@ -0,0 +1,34 @@
+// Copyright 2018 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#ifdef _WIN32
+#include <windows.h>
+
+#include <wincon.h>
+#endif
+
+#include "citra_qt/debugger/console.h"
+#include "citra_qt/ui_settings.h"
+
+namespace Debugger {
+void ToggleConsole() {
+#ifdef _WIN32
+    if (UISettings::values.show_console) {
+        if (AllocConsole()) {
+            freopen_s((FILE**)stdin, "CONIN$", "r", stdin);
+            freopen_s((FILE**)stdout, "CONOUT$", "w", stdout);
+            freopen_s((FILE**)stderr, "CONOUT$", "w", stderr);
+        }
+    } else {
+        if (FreeConsole()) {
+            // In order to close the console, we have to also detach the streams on it.
+            // Just redirect them to NUL if there is no console window
+            freopen_s((FILE**)stdin, "NUL", "r", stdin);
+            freopen_s((FILE**)stdout, "NUL", "w", stdout);
+            freopen_s((FILE**)stderr, "NUL", "w", stderr);
+        }
+    }
+#endif
+}
+} // namespace Debugger