Add chainl1 to the ParserK module

[harendra-kumar]

{-# INLINE chainl1 #-}
chainl1 :: ParserK b IO a -> ParserK b IO (a -> a -> a) -> ParserK b IO a
chainl1 p op = p >>= go

    where

    go l =
        step l <|> pure l
    step l = do
        c <- op
        r <- p
        go (c l r)