Lower the flatness threshold from upem/8 to upem/14, making the
auto-hinter accept shorter elements.
Synchronize flat/round stem selection algorithm with blue zone code.
* src/autofit/aflatin.c (FLAT_THRESHOLD): New macro.
(af_latin_metrics_init_blues): Use it.
(af_latin_hints_compute_segments): Collect information on maximum
and minimum coordinates of `on' points; use this to add a constraint
for the flat/round decision similar to
`af_latin_metrics_init_blues'.
15e2a4f790