All headings now have a uniform color.
Level-1 headings no longer set `w:themeShade="B5"`.
Level-2 headings are now 14 point rather than 16 point.
Level-3 headings are now 12 point rather than 14 point.
Level-4 headings are italic rather than bold.
Closes#5820.
This commit prevents custom styles on divs and spans from overriding
styles on certain elements inside them, like headings, blockquotes,
and links. On those elements, the "native" style is required for the
element to display correctly. This change also allows nesting of
custom styles; in order to do so, it removes the default "Compact"
style applied to Plain blocks, except when inside a table.
...in numbering.xml. This caused pandoc-produced docx files to
be uneditable using Word Online.
The problem was that recent versions of reference.docx include
samples of various kinds of text, including lists. The
numering elements for these were getting copied over to
the new docx, where they clashed with the autogenerated
elements produced by pandoc. This didn't confuse Desktop
Word, but it did confuse Word Online.
Closes#5358.
* docx writer: support custom properties. Solves the writer part of #3024.
Also supports additional core properties: `subject`, `lang`, `category`,
`description`.
* odt writer: improve standard properties, including the following core properties:
`generator` (Pandoc/VERSION), `description`, `subject`, `keywords`,
`initial-creator` (from authors), `creation-date` (actual creation date).
Also fix date.
* pptx writer: support custom properties. Also supports additional core
properties: `subject`, `category`, `description`.
* Includes golden tests.
* MANUAL: document metadata support for docx, odt, pptx writers
