Support landscape pages in Word outputs

[chrisfenner]

We should try to make the Word output more similar to the PDF output by supporting landscape orientation pages.

I made a little progress on this, but had to set it aside.

These Pandoc lua elements will manipulate section breaks and page orientations.

local wordStartLandscape = pandoc.RawBlock(
    'openxml',
    '<w:pPr><w:sectPr><w:pgSz w:w="12240" w:h="15840"/></w:sectPr></w:pPr><w:lastRenderedPageBreak/>'
)

local wordEndLandscape = pandoc.RawBlock(
    'openxml',
    '<w:br w:type="page"/><w:pPr><w:sectPr><w:pgSz w:w="15840" w:h="12240" w:orient="landscape"/></w:sectPr></w:pPr><w:p>TEST</w:p><w:lastRenderedPageBreak/>'
)