Update Windows doc: GHC is no longer needed for hsc2hs, and there's a workaround for Happy.
Update Windows doc: GHC is no longer needed for hsc2hs, and there's a
workaround for Happy.

FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs