added a snake game example and fixed a small bug in the compiler

tests/with_else_if_shorthand.expected

@@ -0,0 +1,4 @@
+neg
+zero
+small
+big

tests/with_else_if_shorthand.sl

@@ -0,0 +1,23 @@
+import stdlib/stdlib.sl
+
+word classify
+    with n in
+        n 0 < if
+            "neg" puts
+        else n 0 == if
+            "zero" puts
+        else n 10 < if
+            "small" puts
+        else
+            "big" puts
+        end
+    end
+end
+
+word main
+    -1 classify
+    0 classify
+    3 classify
+    20 classify
+    0
+end