Thematic breaks don't interrupt paragraphs

[llimllib]

GFM Spec Reference

Per the GFM spec (§4.1 Thematic breaks):

Thematic breaks can interrupt a paragraph:

Example 28 from spec:

Foo
***
bar

Expected HTML:

<p>Foo</p>
<hr />
<p>bar</p>

Reproduction

Stars, underscores, and spaced variants all fail to interrupt a paragraph:

Foo
***
bar

Foo
___
bar

Foo
* * *
bar

Note: --- works because it's treated as a setext heading underline, not because thematic break interruption is implemented.

Actual Output

The *** is treated as inline emphasis markup (* italic containing empty string, then literal *), and the whole thing becomes one paragraph. Similarly ___ is treated as underscore emphasis, and * * * as alternating italic markers.

Root Cause

handle_in_paragraph() does not check for thematic breaks. It only checks for: blank lines, setext heading underlines, fenced code blocks, and table delimiter rows. The is_horizontal_rule() check only happens in handle_ready_state().

This is the same class of bug as #39 (code fences not interrupting paragraphs).