[HarfBuzz] Streamlining hb_font_t some more

[Khaled Hosny]

On Thu, Oct 08, 2015 at 11:54:09AM -0400, Behdad Esfahbod wrote:
>                                                               So, from my
> point of view, you should NOT use this for line height calculation.  You
> should just use the typographical ascender/descender of the font and hence not
> need glyph bounding boxes in Sile at all.

Yes please, an approach similar to what browsers do would be much
appreciated. TeX way of handling interline spacing has always been
cumbersome and confusing (not that I know exactly what SILE do now, but
the further from TeX way here the better).

Regards,
Khaled