Fixed bug with intraword emphasis.

Closes #1066.
ConTeXt writer:  Use setupcaption to separate style from content.

Instead of adding 'nunumber' every time we place a figure...

Closes #1067.
EPUB writer:  Ensure that same identifier is used throughout.

If dc:identifier is given in metadata, we use that; otherwise
we use a random uuid.

Closes #1044.
EPUB writer:  Don't include node for cover.xhtml if no cover!
HTML writer:  Handle csl flipflopping spans (csl-no-emph, etc.)
LaTeX writer:  Handle csl flipflopping spans (csl-no-emph, etc.)
Docx writer:  Implemented csl flipflopping spans.