Add remaining haskell book exercises

Haskell-book/13/Palindrome.hs

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+module Palindrome where
+
+import Control.Monad
+import Data.Char
+import System.Exit
+
+format :: String -> String
+format s = filter (\x -> x >= 'a' && x <= 'z') (map toLower s)
+
+palindrome :: IO ()
+palindrome = forever $ do
+    line1 <- getLine
+    case ((format line1) == (format $ reverse line1)) of
+      True -> putStrLn "It's a palindrome!"
+      False -> do
+          putStrLn "Nope!"
+          exitSuccess
+
+main :: IO ()
+main = palindrome