[Fix] parsing html node ending correctly

[mishig25]

This PR:

1. Reverts changes in [Fix] trl doc build #416. As written in the comment here, my initial assumption of sveltekit http error 500 being not critical was wrong
2. Escape HTML heading node correctly

<h3 id="id">My heading</h3>
Some markdown paragraph

get interpreted as one big html node by marked (see AST here). We would need space between them (see here).
Below is how it should look like

<h3 id="id">My heading</h3>

Some markdown paragraph

cc: @Wauplin