A stable version (otherwise I would have talked about the CVS).
Looking into the CHANGES file you can find the following for 2.1.10:
- A new API in FT_BITMAP_H (`FT_Bitmap_New', `FT_Bitmap_Convert',
`FT_Bitmap_Copy', `FT_Bitmap_Embolden', `FT_Bitmap_Done') has been
added. Its use is to convert an FT_Bitmap structure in 1bpp,
2bpp, 4bpp, or 8bpp format into another 8bpp FT_Bitmap, probably
using a different pitch, and to further manipulate it.
- A new API `FT_Outline_Embolden' (in FT_OUTLINE_H) gives finer
control how outlines are embolded.
- `FT_GlyphSlot_Embolden' (in FT_SYNTHESIS_H) now handles bitmaps
also (code contributed by Chia I Wu). Note that this function is
still experimental and may be replaced with a better API.
Does this answer the question?