Docx Reader: Fix font style parsing.

Before we just checked for the existence of a tag. Now, we make sure to
check for its on/off value.
Docx reader: Add "BlockQuotation" to divs list.
Docx reader: accept explicit "Italic" and "Bold" rStyles.

Note that "Italic" can be on, and, from the last commit, `<w:i>` can be
present, but be turned off. In that case, the turned-off tag takes
precedence. So, we have to distinguish between something being off and
something not being there. Hence, isItalic, isBold, isStrike, and
isSmallCaps have become Maybes.
Docx reader: Check for null-id'd anchors too.

Otherwise they get left dangling in the document.
Docx: More robust handling of multiple bookmarks in header.
Docx Reader: Trim line breaks from the beginning and end of Section
Headers.

We might also want to do this elsewhere (for pars, for example).
Docx: Reducible forgot about smallcaps
Merge pull request #1529 from jkr/dunning-fixes

Fixes from contributed document