Added clear:left to notes DIV

Resolves an issue where the first label (e.g., first bullet or first
number) of a list would wrap to the right side of the window and be
hidden under the clock element.
Support for multiple elements with same data-fragment-index

When multiple elements are specified with the same data-fragment-index,
they are all shown or hidden at once.
add data-start-indexv #427
merge notes float fix and support for multiple fragments with same index
fix previousFragment, was hiding in reverse order #435
upgrade to 2.5.0
-ms-touch-action for #450
float fix in notes-server plugin
viewport meta to fit notes window on ipad
initial implentation of preview frame, add semi-fade fragment style, data-full-height support
support vertical align of slides with absolute children
Use Math.floor instead of parseInt to avoid problems with very small numbers like 2e-10
started the new per-slide background implementation (#453)
add test directory and simple test document for per-slide backgrounds (#453)
don't transition to first slide background (#453)
support for optional background property overrides (#453)
linear sliding transition option for full page backgrounds (#453)
allow control over background color when using images (#453)
update background test, documented slide backgrounds in readme (#453)
update example deck to use slide backgrounds (#453)