[feat] support the variadic `(arg...)` argument extension for CPP macros

[Tal500]

It would be helpful if simplecpp will support variadic argument extension of named variadic in macro.
From https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html:

If your macro is complicated, you may want a more descriptive name for the variable argument than VA_ARGS. CPP permits this, as an extension. You may write an argument name immediately before the ‘...’; that name is used for the variable argument. The eprintf macro above could be written :

#define eprintf(args...) fprintf (stderr, args)

Right now, we are forced to convert this code to:

#define eprintf(...) fprintf (stderr, __VA_ARGS__)

[Tal500]

My fault, it is already supported