Provide binary compatible with Windows 7

[moi15moi]

Aegisub is compabitle with Windows 7, but we need to disabled XAudio2 (-Dxaudio2=disabled). See meson.build.

Currently, in the release section you provide binary with XAudio2 enabled, so it can only run on Windows 8 or more.
Here is the error that we get if we try to open aegisub on Windows 7:

I don't know what if your opinion with supporting EOL OS, but since aegisub can technically run on Windows 7, it would be a plus to provide binary in the future release so the user don't have to use Aegisub 3.2.2 which hasn't have all the nice feature of this fork.