Modified setext heading spec to allow multiline headings.

Text like

    Foo
    bar
    ---
    baz

is now interpreted as heading + paragraph, rather than
paragraph + thematic break + paragraph.

Existing implementations diverge quite a bit on this
case, with several interpretations:

1. paragraph, heading, paragraph
2. paragraph, break, paragraph
3. paragraph containing literal `---`
4. heading, paragraph

Interpretation 4 seems most natural, and it opens up an expressive
possibility otherwise closed off -- multiline headings.

Authors who want interpretation 2 can use a form that can't be
interpreted as a setext heading line, e.g.

    Foo
    bar
    * * *
    baz

or insert blank space around the thematic break.

Authors who want interpretation 3 can use backslash escapes.

Authors who want interpretation 1 can put a blank line
after the first paragraph.

0 files changed, 0 insertions, 0 deletions