[PATCH 1 of 7 V2] util: add a macro initializing CPython modules

[Jun Wu]

Excerpts from Yuya Nishihara's message of 2017-05-14 12:57:57 +0900:
> > +        (void)postinit; \

This line could be changed to:
  
               if ((postinit) == -1) \
                       return; \

> > +    }
> > +#endif
> 
> Maybe I'm a bit conservative about a macro use, but my concern here is,
> it's so easy to make postinint never be called.
> 
>   PYMODULEINIT(parsers, methods, parsers_doc, 1, check_python_version(),
>                module_init)

Then it will get a warning: comparison between pointer and integer.

I think the benefit of code de-duplication is worth a complex marco. The
code using the macro won't get changed frequently so I won't worry too much
about it being used wrongly.