Incorrect description of FT_GASP_SYMMETRIC_SMOOTHING

[piotrunio-2004]

In https://www.freetype.org/freetype2/docs/reference/ft2-gasp_table.html#ft_gasp_xxx ,

FT_GASP_SYMMETRIC_SMOOTHING

If set, smoothing along multiple axes must be used with ClearType.

This is entirely incorrect.

From the observed behaviour of Microsoft ClearType renderers, the behaviour is as following:

If set, 6×5 or 6×1 oversampling may be used. If unset, 6×1 oversampling is always used.

This in turn roughly translates to FreeType language to the following:

If set, smoothing along multiple axes may or may not be used with ClearType.

If unset, smoothing along multiple axes should not be used with ClearType.

The sentence "If set, smoothing along multiple axes must be used with ClearType." is therefore incorrect and should be changed.