Use spaces instead of tab character

[msakai]

How about replacing tab characters with spaces?

Recent GHC warns tab character usage [-Wtabs]. E.g.

haskell_cudd/Cudd/C.hs:116:1: warning: [-Wtabs]
    Tab character found here, and in 27 further locations.
    Please use spaces instead.
    |
116 |         c_cuddReadOne :: Ptr CDDManager -> IO (Ptr CDDNode)
    | ^^^^^^^^