Scale images to fit the page for DOCX

Images that are bigger than the page were truncated. This will now
scale them if they are larger than the page. The scale is currently
hardcoded with Word "letter" defaults (page size and margins)
Docx reader: Fix spacing issue.

Previously spaces at the beginning of Emph/Strong/etc were kept
inside. This makes sure they are moved out.
Change head/tail to pattern guards.
Merge pull request #1510 from jkr/spacefix

Docx reader: Fix spacing issue.
Merge pull request #1512 from mpickering/master

Improved EPUB Tests
EPUB Writer: Added explicit imports
EPUB reader: Fixed bug where filepaths weren't sufficiently normalised
EPUB Writer: Added page-progression-direction meta field
Updated README with information about  EPUB meta element
EPUB Reader: Can now parse multiple meta data fields
Docx Fonts: Derives Show and Eq
Docx Parse: Improved font recognition when specified in rFonts element
Docx Parse: Updated tests
Merge pull request #1518 from jkr/fontsmore

Symbol font improvements from mpickering.
Merge pull request #1516 from mpickering/epubmetadata

EPUB improvements
README:  Added needed blanklines in definition list.

Thanks @mpickering for noticing this.
EPUB Reader: Fixed another normalisation problem..
TeX Writer: Write hyperdef and label for identifiers on Div blocks
Docx reader: handle empty reducibles.
Merge pull request #1365 from gbataille/docx-margin

Scale images to fit the page for DOCX