Allows lazy-loaded (i.e. data-src) iframes to be preloaded when they
come within the viewDistance, rather than once they're visible.

Fixed not bing able to follow same inner links twice with history:false

Scenario:

- history set to false in Reveal’s config
- follow anchor to `/#someid`
- navigate to other sections
- follow anchor to same section `/#someid`

This does not work as the hash has not changed.

This fix removes the hash from the URL when navigating

notes plugin: callRevealApi wants apply, not call

demo.html - Added Linux instructions for zoom

Fixed a couple of typos

remove unused `isPrintingPDFFragments` function

Revert "impove randomness"