_Almost_ fully C99 compatible `##__VA_ARGS__` and `__VA_OPT__()` alternative.
The compiler needs to support empty `__VA_ARGS__` (not to C99 spec) for this to work, though
all compilers tested had no issue with that (even those with partial C99 support, like lacc)

### Usage and hacking

Replace `__VA_ARGS__` with `VA_OPT_C(__VA_ARGS__)`:

```
#define prlog(f, ...) fprintf(stderr, f /* no comma here */ VA_OPT_C(__VA_ARGS__))
```

You can also define your own top level macro, `I_MAKE_TEST()` and the test macros themselves to 
add a lot more conditional functionality based on `__VA_ARGS__` being empty or not.