[Freetype] Render with an outline

[Fu Chen]

HI!
What I try to do is rendering small size character(10 or 12 points) on an 
image. We can't know what's the image's color, so simply render string with one 
color maybe hide the character in the background and make it difficult to 
recognize.
Now, I render it four time with another color at (x-1, y-1), (x-1, y+1), (x+1, 
y-1), (x+1,y+1)  to draw an outline for the character. But I think it will harm 
the efficiency. 
Is there any quick and elegant way to get this effect?