Yet another at3+ encoder/decoder

[freefive]

Could you test r3075 and place at3tool.exe under lib/windows-x86 or lib/windows-amd64? I've added basic support for this tool, but could not test it.

gid15，test with r3076，the bgm will disappear
DecodeAudio.bat should be modified to this

Code:

lib\windows-amd64\at3tool.exe -d -repeat 1 %3 %2

plus some stereo bgms seems not decodable with this tool but decodable with atrac3plus2wav.exe (oma file, namely %1)
tested with F/E CCC