Render Markdown lists correctly

[sk22]

Closes #152

[sk22]

(ignore the bold thing that's actually meant to be rendered in italic – but not in this pull request)

[grishka]

Hm. But Markdown isn't an officially supported Mastodon feature 🤔

[sk22]

well, people come across posts using "advanced" html tags, including lists, all the time.

mastodon for web renders this

LIST HEADER

* item 1
* item 2

LIST FOOTER

<p>LIST HEADER<p>
<ul>
  <li>item 1</li>
  <li>item 2</li>
</ul>
<p>LIST FOOTER</p>

like this:

…which is still readable.

mastodon for android renders it like this:

[sk22]

my pull request can be easily adapted to archive what you see on mastodon web; by

• removing the "head" switch-case for "p" (which ensures the empty line after lists/non-paragraphs)
• removing the "head" switch-case for "li"
• moving the "tail" case for "li" outside the !openSpans.isEmpty() block

edit: i've simplified the implementation since

[sk22]

would look like this. you can add commits to this PR if you want to

[sk22]

found an issue with my implementation: list items will always append a line break, even if there's nothing after them – resulting in an empty line at the end of the SpannableStringBuilder

[sk22]

okay, fixed it – also, the implementation feels much cleaner now

[sk22]

… and since #152 also applies to other block elements, like <blockquote>, it's probably smart to insert spaces (just like after <p> elements), so i changed the logic a bit.

[sk22]

Hm. But Markdown isn't an officially supported Mastodon feature 🤔

it is now: mastodon/mastodon#23913