It is easier to check directions using flags than integer values.
* src/pshinter/pshalgo.h (PSH_Dir): Redefine directions.
(PSH_PointRec): Use them as an enum type.
* src/pshinter/pshalgo.c (psh_compute_dir): Modify return type.
(psh_glyph_init, psh_hint_table_find_strong_points,
psh_glyph_find_blue_points): Update users.