Fix text and add more documentation.

Former-commit-id: 1c9e6e964707ccd424aff914811e67597732c91c

examples/doc_mkText.hs

@@ -0,0 +1,15 @@
+#!/usr/bin/env stack
+-- stack runghc --package reanimate
+{-# LANGUAGE OverloadedStrings #-}
+module Main (main) where
+
+import           Reanimate
+import           Reanimate.Builtin.Documentation
+import qualified Data.Text as T
+
+main :: IO ()
+main = reanimate $ docEnv $ mkAnimation 2 $ \t ->
+  scale 2 $
+  withStrokeWidth 0.05 $
+  mkText (T.take (round $ t*15) "text")
+