With this patch, the blocks in a markdown document render a vector of
lines. These lines get concatenated in Document::render_to_terminal, so
this does not change any external APIs of LibMarkdown.
This change makes it possible to indent individual lines in the rendered
markdown. So, rendering blockquotes in a similar way to code blocks :^)
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
From the commonmark spec:
A list is loose if any of its constituent list items are separated by
blank lines, or if any of its constituent list items directly contain
two block-level elements with a blank line between them. Otherwise a
list is tight. (The difference in HTML output is that paragraphs in a
loose list are wrapped in <p> tags, while paragraphs in a tight list are
not.)
