Use gifs to improve documentation. (#21)

Former-commit-id: 40e5ccedcf5d1ca8f0d5cc373ba3b3c4cc2d6c6a

examples/doc_drawBox.hs

@@ -0,0 +1,9 @@
+#!/usr/bin/env stack
+-- stack runghc --package reanimate
+module Main(main) where
+
+import Reanimate
+import Reanimate.Builtin.Documentation
+
+main :: IO ()
+main = reanimate $ docEnv drawBox