Chromium users need to check Background graphics option when printing.

Add the grunt-cli as a dependency instead of assuming global grunt.

remove redundant spaces.

Fix spelling error in print-pdf plugin

prevents XSS vulnerability (see https://github.com/janl/mustache.js/pull/388)

Add an option to auto-slide right only

Auto-sliding will now use the method specified in the config if it is
a function or default to navigateNext.

stops parallax failing if only the single horizontal slide and multiple vertical

When the autoSlideRight config option is active, the auto-sliding
will always navigate to the right and never down even if slides are
present there. This allows hidden "bonus slides" in presentations
which can be displayed as needed but won't show up automatically.

check for 0 division, stops parallax failing if only the single horizontal slide and multiple vertical