Add languages to "pre" tags (HTML and Markdown) #1118

* added `language` to entities when unparsing (both markdown and html)

* added `language` to entities also when parsing (html only)

* Update html.py

* Update markdown.py

* Update markdown.py

* Update markdown.py

Co-authored-by: Dan <14043624+delivrance@users.noreply.github.com>