OpenDocument:  Skip raw HTML.

Previously it was erroneously included as verbatim text.

Closes #1035.
Parsing:  Generalized type of registerHeader, using new typeclasses.

New type classes HasReadeOptions, HasIdentifierList, HasHeaderMap.
These allow certain common functions to be reused even in parsers
that use custom state (instead of ParserState), such as the MediaWiki
reader.

Minor API bump.
MediaWiki reader:  Add automatic header identifiers.
LaTeX reader: Support `\textnormal` as span with class "nodecor".

This is needed for pandoc-citeproc.
Epub Writer: Add cover reference to guide element

Fixes an issue with calibre http://calibre-ebook.com/ putting the
cover at the end of the book if the spine has linear="no".

Apparently this is best practice for other converters as well.

http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm#Section2.6
LaTeX reader:  Parse contents of curly quotes or matched `"` as quotes.
Epub Writer: Add cover reference to guide element (v2)

Avoiding an unnecessary list concatenation.

Fixes an issue with calibre http://calibre-ebook.com/ putting the
cover at the end of the book if the spine has linear="no".

Apparently this is best practice for other converters as well.

http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm#Section2.6
Merge pull request #1061 from heurist/epub_coverLinear

Epub Writer: Refactor unnecessary list ++
Docbook writer:  Hierarchicalize block content in metadata.

Previously headers just disappeared from block-level metadata
when it was used in templates.

Now we apply the 'hierarchicalize' transformation.

Note that a block headed by a level-2 header will turn into
a `<sect1>` element.
MIME:  In looking up extensions, drop the encoding info.

E.g. for 'image/jpg;base64' we should lookup 'image/jpg'.
Shared: Fixed bug in openURL with data: URIs.

Previously the base-64 encoded bytestring was returned.
We now decode it so it's a proper image!

This should fix parsing of data: URLs.
Docx writer:  Use mime type info returned by fetchItem.