Fix rendering of code with <hlcode>
Markdown generated for <hlcode> did not conform to the Commonmark spec and was not compatible with marked 0.6+. Fixes arsnova#101. Fixes GH-89.
Markdown generated for <hlcode> did not conform to the Commonmark spec and was not compatible with marked 0.6+. Fixes arsnova#101. Fixes GH-89.