This can be used by plugins which are concerned with helping the
presenter with their pace.

This can be used by plugins which are concerned with helping the
presenter with their pace.

layout() and thereby layoutSlideContents() is never invoked
when isPrintingPdf() is true so stretch elements are not
sized correctly.
This is ensured now by invoking the layoutSlideContents
from SetupPDF(). There seems no need to scale down
like in other PR's is suggested.

this way a key can be given ability to toggleHelp on and off.  Previously Reveal.showHelp could open the help screen, but no way to close it.

wait for in-slide video/audio to load before playing, reuse same autoplay logic for slide backgrounds

#1770, set 'data-paused-by-reveal' attribute only for the media elements, which are not already in paused state.