Add support for Apple composite glyphs.

* include/freetype/config/ftoption.h
(TT_CONFIG_OPTION_COMPONENT_OFFSET_SCALED): New macro.

* src/truetype/ttgload.c (OVERLAP_COMPOUND, SCALED_COMPONENT_OFFSET,
UNSCALED_COMPONENT_OFFSET): New macros for additional OpenType
glyph loading flags.
(load_truetype_glyph): Implement it.