A QTextDocument can now be written out in Markdown format.
- Add the QTextMarkdownWriter as a private class for now
- Add QTextDocument::toMarkdown()
- QTextDocumentWriter uses QTextMarkdownWriter if setFormat("markdown")
is called or if the file suffix is .md or .mkd
- Add QTextEdit::toMarkdown() and the markdown property
[ChangeLog][QtGui][Text] Markdown (CommonMark or GitHub dialect) is now
a supported format for reading into and writing from QTextDocument.
Change-Id: I663a77017fac7ae1b3f9a400f5cd357bb40750af
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>
