flush stdio from libc

[Suavesito-Olimpiada]

fix #46

What this does is to flush stdio from libc, so the remaining text doesn't stay in the buffer.

[marcom]

This is really necessary when working with libc stdio, would be useful to have this in the library. Maybe running flush_cstdio should be optional though?

Edit: thinking about this some more, maybe it should be enabled always