Fix #993.
Added PDF export setting within PressBooks Custom CSS theme options to enable or disable romanized part numbers.
The other way around.
Merge pull request #48 from bdolor/dev

epub support for WP image rendering service for latex equations, adding LaTeX plugin.
Invisible part setting field.
L18n compliance for pressbooks-book cover page, other l18n fixes.
Colon after copyright in webbook footer.
Initial implementation of invisible parts.
Merge branch 'invisible' into dev
Prince styles for invisible parts.
Part that have content are new linked in TOC on webbooks.
Added 5" x 8" page size for PDFs.
SVG files are now enabled.
Parts with content are now included in back/forward navigation in webbooks.
Don't show invisible parts in back/forward navigation in webbooks.
Extraneous parenthesis.
replacing deprecated wp calls