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.
EPUB writer:  Improved metadata handling.

* Metadata may now be included in YAML blocks in a markdown document.
  For example,

        ---
        title:
        - type: main
          text: My Book
        - type: subtitle
          text: An investigation of metadata
        creator:
        - role: author
          text: John Smith
        - role: editor
          text: Sarah Jones
        identifier:
        - scheme: DOI
          text: doi:10.234234.234/33
        publisher:  My Press
        rights:  (c) 2007 John Smith, CC BY-NC
        ...

* Metadata may still be provided using `--epub-metadata`; it will
  be merged with the metadata in YAML blocks.
* meta tags are used instead of opf attributes for EPUB3.
Documented use of YAML metadata for EPUB.
README: minor reformatting.
Allow specification of epub-cover-image in YAML metadata.
Fixed `cover-image` in EPUB YAML metadata.
Allow "epub2" as synonym for "epub", "html4" for "html".
ConTeXt writer:  Don't hardcode figure/table placement.

Instead, let this be set in the template, using `\setupfloat`.
Thanks to Aditya Mahajan for the suggestion.
Fixed tests for new ConTeXt writer behavior.
ODT writer:  Add `draw:name` attribute to `draw:frame` elements.

This is reported to be necessary to avoid an error from recent
versions of Libre Office when files contain more than one image.

Closes #1069.

Thanks to wmanley for reporting and diagnosing the problem.
Markdown writer:  Fix rendering of tight sublists.

E.g.

    - foo
        - bar
    - baz

Previously a spurious blank line was included before the last item.
Closes #1050.
EPUB writer: Add properties attribute to cover-image item for EPUB v3.
MIME:  Add entry for jfif.
EPUB writer: Simplify imageTypeOf using getMimeType.