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.
u_bitwidth_to_subformat (int bits)
{	static int array [] =
	{	SF_FORMAT_PCM_U8, SF_FORMAT_PCM_16, SF_FORMAT_PCM_24, SF_FORMAT_PCM_32
		} ;

	if (bits < 8 || bits > 32)
		return 0 ;

	return array [((bits + 7) / 8) - 1] ;
} /* bitwidth_to_subformat */

u_bitwidth_to_subformat (int bits)
{	static int array [] =
	{	SF_FORMAT_PCM_U8, SF_FORMAT_PCM_16, SF_FORMAT_PCM_24, SF_FORMAT_PCM_32
		} ;

	if (bits < 8 || bits > 32)
		return 0 ;

	return array [((bits + 7) / 8) - 1] ;
} /* bitwidth_to_subformat */
