Add GitHub Actions

[flibitijibibo]

Required:

• [x] Windows (MSVC)
• [x] Windows (MinGW)
• [x] Wine (MinGW with Win32 backend)
• [x] Linux (can just be ubuntu-latest)
• [x] macOS CMake (TODO: macOS Xcode)
• [ ] iOS/tvOS

Optional:

• [x] FreeBSD (take from SDL)

[flibitijibibo]

Got the obvious ones done just now: https://github.com/FNA-XNA/FAudio/commit/55a8b04a7cfb9fadc69251f889bcdd83fc62c525

Linux doesn't work thanks to outdated SDL, will have to get around that with our own copy I guess!

[flibitijibibo]

MinGW is now done - this is the last of the platforms that I build!