Feat: fenced code blocks

[martin-martin]

Changes the representation of <pre><code> to fenced code blocks instead of indented code blocks in Markdown.

Fenced code blocks allow for user-friendly addition of language syntax, e.g.:

```python
print("hello")
```

Syntax highlighting for these types of fenced code blocks is today widely available and make code snippets more legible.

I therefore suggest to replace this as the default rendering of <pre><code>.

[martin-martin]

Fixes #11

[dlon]

Thanks! I'm not necessarily opposed to the idea. Fenced code blocks are an extension of standard markdown, though, so it may have to be an option.

[dlon]

This will cause any <pre> element to be surrounded with a code fence, not just <pre><code>.

[unexceptable]

For safety and clarity that's not bad, but makes it harder to convert back to html.

Maybe for <pre> we only indent as you already did, but for <code> we backtick explicitly? Then the process to reverse back to html has a method it can follow.

[dlon]

This loop doesn't do anything. I can't remember if lines[i] = line.replace(...) is still necessary, but it's currently not being assigned to lines[i].

[unexceptable]

@dlon

Thanks! I'm not necessarily opposed to the idea. Fenced code blocks are an extension of standard markdown, though, so it may have to be an option.

Unlike other formats markdown doesn't really have an 'official' spec, and fenced code blocks are kinda of the standard across almost all users of markdown for code.

If anything https://commonmark.org/ is probably 'the standard', and does have fenced back tick codeblocks as part of it. :)