Fix Windows unicode paths

[zebrys]

Fix the issue #200 (on Windows).

[evanmiller]

Do we need portable_main applied to the extract_metadata CLI tool also?

[zebrys]

Do we need portable_main applied to the extract_metadata CLI tool also?

@evanmiller Are you talking about the replacement of main by portable_main in src/bin/extract_metadata.c? This is already the case.
Overall, all programs that take possible unicode parameters in input (eg. filenames) should use portable_main (only readstat and extract_metadata seems to need that I guess).

[evanmiller]

Ah yes I was reading the patch too quickly. I will merge it in.