Support platforms other than Windows

Right now, we are trying to run the `pabcnetc.exe` directly, which will only work on platforms that support this executable (Windows mainly).

We should support Mono on other platforms as well.

(Unfortunately, the story about the compiler which highly depends on System.Reflection.Emit on modern .NET runtimes is very complex, and we'll unlikely be able to run it, say, on .NET 6 soon).