Add inc, double, square functions

Unit 1/calculate/change/calcChange.hs

@@ -0,0 +1,19 @@
+calcChange :: (Ord p, Num p) => p -> p -> p
+calcChange owed given = if change > 0
+                        then change
+                        else 0
+    where change = given - owed
+
+inc :: Num a => a -> a
+inc x = x + 1
+
+double :: Num a => a -> a
+double x = x * 2
+
+square :: Num a => a -> a
+square x = x * x
+
+evenOrOdd :: Integral a => a -> a
+evenOrOdd n = if even n
+              then n - 2
+              else 3 * n + 1