This is now the default for pandoc's Markdown.
It allows whitespace between the two parts of a
reference link: e.g.
[a] [b]
[b]: url
This is now forbidden by default.
Closes#2602.
* LaTeX: Load `parskip` before `hyperref`.
According to `hyperref` package's `README.pdf`, page 22, `hyperref` package
should be loaded after `parskip` package.
* Adjust tests for previous change.