Major improvements to the SDL debugging interface, especially on Windows

1. No more separate EXE for the debugger version, the console can be freely opened at any time with ^C, and closed freely without terminating the emulator
2. On all platforms, the SDL emulator window is no longer unresponsive while the debugger is waiting for an input
3. Pressing keys in the emulator window while the debugger is waiting for inputs will trigger a terminal bell
4. Async debugging now supports Windows 7, 8.x, and earlier builds of Windows 10