Add case...of slide, rename slides

VL1/content/VL1_case_of.tex

@@ -0,0 +1,10 @@
+We can also pattern match on the result of a real expression, not just the input. For that, we write:
+
+\begin{haskellcode}
+f :: Int -> Bool
+f x = case x - 2 of
+  2 -> True
+  5 -> True
+  y -> False
+\end{haskellcode}
+This allows more powerful pattern matching, especially when we define our own data structures.