This fixes a bug in 2.0.4, whereby pandoc could not
read the theme files generated with `--print-highlight-style`.
It also fixes some CSS issues involving line numbers.
Highlighted code blocks are now enclosed in a div with class
sourceCode.
Highlighting CSS no longer sets a generic color for pre
and code; we only set these for class `sourceCode`.
This will close#4133 and #4128.
* 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.