Rework ListBlockRenderer and ListItemRenderer to respect node settings

[stefanzweifel]

As discussed in #9 and #10, the package currently does a poor job at respecting the various node settings available in the renderer.

We should refactor both ListBlockRenderer and ListItemRenderer to respect the available node settings and support various list types.

- List Item
- Lst Item

* List Item
* List Item

1. List Item
2. List Item

1) List Item
2) List Item

If possible, it would also be great if we could remove our workaround for multi-line list items we've added in #7 that temporarily adds the string _COMMONMARK_MARKDOWN_RENDERER_LINE_BREAK_ to list items.