So far, multiple notes per slide are only supported if they are
attached to fragments (without fragments, only the first aside notes
element on a slide is displayed).  With this commit, the contents of
all notes on a slide are displayed (except for fragments with notes,
for which, as before, only each fragment's first/single note is
displayed).

new shortcuts; alt+arrow key skips fragments, shift+arrow key jumps to last slide in the given direction #1105

fix(highlight): allow pre fragments

prepend --r- to global style variables

When embedding reveal in a website, this will help avoid global variable conflicts with other frameworks that use global styles via variables.

Implement auto-animate id and restart

markdown plugin improvements

Add an "animateLists" option to the markdown plugin that animates all
lists by default.

Don't waste time constructing a renderer then override it if one is
passed into the options object.

Expose preview management functions

Fix: multiple image-urls in data-background-image