tiny followup to #1103

It works around the current PDF rendering bugs like #1261

The socket.io server at reveal.jit.su has been updated with socket.io
1.x, which means the examples referring to 0.9.x client libraries
no longer work. Update them with URLs for 1.3.5.

Fixes #1276.

For those who can't install Google Chrome (e.g. work network policies) but can use Chromium, Chromium does work for creating the pdf. I updated the readme accordingly. Thanks!

Theming/sky.css has dark gray text on light blue background; not white text

Now the transition isn’t any more „per slide“ but „per movement of a
slide“. So the slide can disappear in another way than it appeared.

To honor the DRY principle repeating patterns have been factored out.
In addition there was an anchor missing in README.md.