src/ : Move to a variable length header buffer

Previously, the `psf->header` buffer was a fixed length specified by
`SF_HEADER_LEN` which was set to `12292`. This was problematic for
two reasons; this value was un-necessarily large for the majority
of files and too small for some others.

Now the size of the header buffer starts at 256 bytes and grows as
necessary up to a maximum of 100k.
log_putchar (SF_PRIVATE *psf, char ch)
{	if (psf->parselog.indx < SIGNED_SIZEOF (psf->parselog.buf) - 1)
	{	psf->parselog.buf [psf->parselog.indx++] = ch ;
		psf->parselog.buf [psf->parselog.indx] = 0 ;
		} ;
	return ;
} /* log_putchar */

log_putchar (SF_PRIVATE *psf, char ch)
{	if (psf->parselog.indx < SIGNED_SIZEOF (psf->parselog.buf) - 1)
	{	psf->parselog.buf [psf->parselog.indx++] = ch ;
		psf->parselog.buf [psf->parselog.indx] = 0 ;
		} ;
	return ;
} /* log_putchar */
