[gabesgh]

Description

Fixes #845.

When a list item comes right after an indented paragraph or nested list of the previous item, with no blank line in between, it was swallowed into that paragraph as a lazy continuation line.

ListIndentProcessor now ends the indented block at the first unindented line that starts another item of the same list. Those items continue the list as tight items, because no blank line comes before them (the same as Markdown.pl).

Unchanged:

• Lazy continuation lines, and the First line of a paragraph / - second line example from the issue.
• With sane_lists, a marker of the other list type is still treated as text.

One behaviour change: a horizontal rule or header right after those items now ends the list, the same as it already does for a list at the top level. Before, it ended up inside the previous item.

Not covered:

• The same pattern one level deeper, where a nested item comes after a nested item's indented paragraph.
• The equivalent case with def_list.

I'm happy to look at those separately.

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