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.
Allow override of HTML escaping in code blocks

This way, authors can use HTML for special formatting.
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