[Regression 0.7 -> 1.0] code blocks are not highlighted anymore

[actionless]

Code block (```) is not anymore highlighted and neither have any HTML class which could be used for a custom CSS.

0.7:

1.0:

[brrd]

Yes. It's intended. Codeblocks styling introduced very heavy performance issues (see #274) so I decided to remove it until we code something better. I'll create an issue to keep a track of this.

[actionless]

thanks!