Add Haskell solutions for Problems 4, 5, 6, 7

Haskell/p005.hs

@@ -0,0 +1,13 @@
+-- 2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+--
+-- What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+
+lcmm :: (Integral n) => [n] -> n
+lcmm values
+    | length values == 2    = lcm (head values) (last values)
+    | otherwise             = lcm (head values) (lcmm (tail values))
+
+main = do
+    let result = lcmm [1..20]
+    putStrLn $ "Project Euler, Problem 5\n"
+        ++ "Answer: " ++ (show result)