Improve README examples (#68)

- Move examples higher, above any technical details.
- Use a consistent off-white background color.
- Use more interesting and less trivial examples.
- Play at 50fps rather than 25fps.
- Host offsite (imgur) as to not take up repo space.
- Link to source file for each example.

Former-commit-id: 7e62a3a1ca99e9abc5781568ff920066c94783ee

examples/tut_glue_latex.hs

@@ -25,7 +25,7 @@ latexExample = sceneAnimation $ do
     -- Draw equation
     play $ drawAnimation strokedSvg
     sprites <- forM glyphs $ \(fn, _, elt) ->
-      newSpriteA $ animate $ const $ fn elt
+      newSpriteSVG $ fn elt
     -- Yoink each glyph
     forM_ (reverse sprites) $ \sprite -> do
       spriteE sprite (overBeginning 1 $ aroundCenterE $ highlightE)