Add colormaps to documentation.

Former-commit-id: d9db76c4f0715800ef6f94e6618d6682a2c8112b

examples/doc_sinebow.hs

@@ -0,0 +1,18 @@
+#!/usr/bin/env stack
+-- stack runghc --package reanimate
+module Main(main) where
+
+import Codec.Picture
+import Reanimate
+import Reanimate.Builtin.Documentation
+
+main :: IO ()
+main = reanimate $ docEnv $ animate $ const $ mkColorMap sinebow
+
+mkColorMap :: (Double -> PixelRGB8) -> SVG
+mkColorMap f = center $ scaleToSize screenWidth screenHeight $ embedImage img
+  where
+    width = 256
+    height = 1
+    img = generateImage pixelRenderer width height
+    pixelRenderer x _y = f (fromIntegral x / fromIntegral (width-1))