fix #62, make c2hs support Haddock for function arguments

This function definition:

     {# fun f1
       { `Int' -- ^ This is a multiline
               -- comment for
               -- para1
       , `Int'
       , `Int' -- ^ comment for para3
       } -> `Int' -- ^ multiline
                 -- comment for
                 -- result
    #}

will now generate type signature as following:

    f1 :: (Int) --  ^ This is a multiline  comment for  para1
     -> (Int) -> (Int) --  ^ comment for para3
     -> IO ((Int)) --  ^ multiline  comment for  result