Find a config file if possible.

def _find_file(f):
        """Find a config file if possible."""
        if os.path.isabs(f):
            return f
        else:
            for d in Config._dirs:
                _f = os.path.join(d, f)
                if os.path.isfile(_f):
                    return _f
            raise FiggypyError(
                "could not find configuration file {} in dirs {}"
                .format(f, Config._dirs)
            )