Add atrac3plus filter for win32

I write a filter for dshow and make it work as the similar way as ffmpeg. Based on some tests, the filter should work fine on win32 system now. And it won't crash now even the filter doesn't work.
To make it work, you need to register the filter in filter/lib/, I'm not sure how to make it work on x64.
By the way, if you want to compile the filter by yourself, you must have DirectShow SDKs.