Parse code blocks in Markdown

[rikhuijzer]

Issue by @AbhimanyuAryan.

Currently, Markdown with embedded code blocks are not parsed correctly. For example,

md"""
Lorem ipsum:

```julia
julia> x = 1
1

julia> x + 1
2
```
"""

does not become a code block in the output

[AbhimanyuAryan]

it becomes

<div class="markdown"><pre><code class="language-julia"> julia> x = 1 .... </div>

I idea is to control <pre> to output something like <pre class="mangoes"> @rikhuijzer