Add data types required for the forthcoming 'sdf' module.

* include/freetype/freetype.h (FT_Render_Mode): Add new render mode
`FT_RENDER_MODE_SDF`, which will be used to generate SDF.

* include/freetype/ftimage.h (FT_Pixel_Mode): Add new pixel mode
`FT_PIXEL_MODE_GRAY16`, which will be the output of the 'sdf'
module.
(FT_RASTER_FLAG_SDF): New raster flag to be used internally by the
'sdf' module.

* include/freetype/fttypes.h (FT_F6Dot10): New data type.
4 files changed