Add Case control flow structre and remove css class

elixir.md

@@ -105,7 +105,6 @@ Pattern matching works in function parameters too.
 
 Control flow
 ------------
-{: .-three-column}
 
 ### If
 
@@ -116,6 +115,18 @@ else
   "This will"
 end
 ```
+### Case
+
+```elixir
+case {1, 2, 3} do
+  {4, 5, 6} ->
+    "This clause won't match"
+  {1, x, 3} ->
+    "This clause will match and bind x to 2 in this clause"
+  _ ->
+   "This clause would match any value"
+end
+```
 
 ### Cond