Comply with CommonMark 0.31.2

[Witiko]

In #220, @lostenderman added support for CommonMark 0.30. On 2024-01-28, @jgm released CommonMark 0.31.2.

We should review the diff of the spec and the test cases:

$ diff \
> <(wget -qO - https://spec.commonmark.org/0.30/spec.json | grep -Ev '"(start_line|end_line|example)": ')
> <(wget -qO - https://spec.commonmark.org/0.31.2/spec.json | grep -Ev '"(start_line|end_line|example)": ')

98,99c98,99
<     "markdown": "<http://example.com?find=\\*>\n",
<     "html": "<p><a href=\"http://example.com?find=%5C*\">http://example.com?find=\\*</a></p>\n",
---
>     "markdown": "<https://example.com?find=\\*>\n",
>     "html": "<p><a href=\"https://example.com?find=%5C*\">https://example.com?find=\\*</a></p>\n",
1723,1724c1723,1724
<     "markdown": "`<http://foo.bar.`baz>`\n",
<     "html": "<p><code>&lt;http://foo.bar.</code>baz&gt;`</p>\n",
---
>     "markdown": "`<https://foo.bar.`baz>`\n",
>     "html": "<p><code>&lt;https://foo.bar.</code>baz&gt;`</p>\n",
1728,1729c1728,1729
<     "markdown": "<http://foo.bar.`baz>`\n",
<     "html": "<p><a href=\"http://foo.bar.%60baz\">http://foo.bar.`baz</a>`</p>\n",
---
>     "markdown": "<https://foo.bar.`baz>`\n",
>     "html": "<p><a href=\"https://foo.bar.%60baz\">https://foo.bar.`baz</a>`</p>\n",
1767a1768,1772
>     "markdown": "*$*alpha.\n\n*£*bravo.\n\n*€*charlie.\n",
>     "html": "<p>*$*alpha.</p>\n<p>*£*bravo.</p>\n<p>*€*charlie.</p>\n",
>     "section": "Emphasis and strong emphasis"
>   },
>   {
2393,2394c2398,2399
<     "markdown": "**a<http://foo.bar/?q=**>\n",
<     "html": "<p>**a<a href=\"http://foo.bar/?q=**\">http://foo.bar/?q=**</a></p>\n",
---
>     "markdown": "**a<https://foo.bar/?q=**>\n",
>     "html": "<p>**a<a href=\"https://foo.bar/?q=**\">https://foo.bar/?q=**</a></p>\n",
2398,2399c2403,2404
<     "markdown": "__a<http://foo.bar/?q=__>\n",
<     "html": "<p>__a<a href=\"http://foo.bar/?q=__\">http://foo.bar/?q=__</a></p>\n",
---
>     "markdown": "__a<https://foo.bar/?q=__>\n",
>     "html": "<p>__a<a href=\"https://foo.bar/?q=__\">https://foo.bar/?q=__</a></p>\n",
2498,2499c2503,2504
<     "markdown": "[link](#fragment)\n\n[link](http://example.com#fragment)\n\n[link](http://example.com?foo=3#frag)\n",
<     "html": "<p><a href=\"#fragment\">link</a></p>\n<p><a href=\"http://example.com#fragment\">link</a></p>\n<p><a href=\"http://example.com?foo=3#frag\">link</a></p>\n",
---
>     "markdown": "[link](#fragment)\n\n[link](https://example.com#fragment)\n\n[link](https://example.com?foo=3#frag)\n",
>     "html": "<p><a href=\"#fragment\">link</a></p>\n<p><a href=\"https://example.com#fragment\">link</a></p>\n<p><a href=\"https://example.com?foo=3#frag\">link</a></p>\n",
2623,2624c2628,2629
<     "markdown": "[foo<http://example.com/?search=](uri)>\n",
<     "html": "<p>[foo<a href=\"http://example.com/?search=%5D(uri)\">http://example.com/?search=](uri)</a></p>\n",
---
>     "markdown": "[foo<https://example.com/?search=](uri)>\n",
>     "html": "<p>[foo<a href=\"https://example.com/?search=%5D(uri)\">https://example.com/?search=](uri)</a></p>\n",
2683,2684c2688,2689
<     "markdown": "[foo<http://example.com/?search=][ref]>\n\n[ref]: /uri\n",
<     "html": "<p>[foo<a href=\"http://example.com/?search=%5D%5Bref%5D\">http://example.com/?search=][ref]</a></p>\n",
---
>     "markdown": "[foo<https://example.com/?search=][ref]>\n\n[ref]: /uri\n",
>     "html": "<p>[foo<a href=\"https://example.com/?search=%5D%5Bref%5D\">https://example.com/?search=][ref]</a></p>\n",
2968,2969c2973,2974
<     "markdown": "<http://foo.bar.baz/test?q=hello&id=22&boolean>\n",
<     "html": "<p><a href=\"http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean\">http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean</a></p>\n",
---
>     "markdown": "<https://foo.bar.baz/test?q=hello&id=22&boolean>\n",
>     "html": "<p><a href=\"https://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean\">https://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean</a></p>\n",
2993,2994c2998,2999
<     "markdown": "<http://../>\n",
<     "html": "<p><a href=\"http://../\">http://../</a></p>\n",
---
>     "markdown": "<https://../>\n",
>     "html": "<p><a href=\"https://../\">https://../</a></p>\n",
3003,3004c3008,3009
<     "markdown": "<http://foo.bar/baz bim>\n",
<     "html": "<p>&lt;http://foo.bar/baz bim&gt;</p>\n",
---
>     "markdown": "<https://foo.bar/baz bim>\n",
>     "html": "<p>&lt;https://foo.bar/baz bim&gt;</p>\n",
3008,3009c3013,3014
<     "markdown": "<http://example.com/\\[\\>\n",
<     "html": "<p><a href=\"http://example.com/%5C%5B%5C\">http://example.com/\\[\\</a></p>\n",
---
>     "markdown": "<https://example.com/\\[\\>\n",
>     "html": "<p><a href=\"https://example.com/%5C%5B%5C\">https://example.com/\\[\\</a></p>\n",
3033,3034c3038,3039
<     "markdown": "< http://foo.bar >\n",
<     "html": "<p>&lt; http://foo.bar &gt;</p>\n",
---
>     "markdown": "< https://foo.bar >\n",
>     "html": "<p>&lt; https://foo.bar &gt;</p>\n",
3048,3049c3053,3054
<     "markdown": "http://example.com\n",
<     "html": "<p>http://example.com</p>\n",
---
>     "markdown": "https://example.com\n",
>     "html": "<p>https://example.com</p>\n",
3118,3124c3123,3124
<     "markdown": "foo <!-- this is a\ncomment - with hyphen -->\n",
<     "html": "<p>foo <!-- this is a\ncomment - with hyphen --></p>\n",
<     "section": "Raw HTML"
<   },
<   {
<     "markdown": "foo <!-- not a comment -- two hyphens -->\n",
<     "html": "<p>foo &lt;!-- not a comment -- two hyphens --&gt;</p>\n",
---
>     "markdown": "foo <!-- this is a --\ncomment - with hyphens -->\n",
>     "html": "<p>foo <!-- this is a --\ncomment - with hyphens --></p>\n",
3128,3129c3128,3129
<     "markdown": "foo <!--> foo -->\n\nfoo <!-- foo--->\n",
<     "html": "<p>foo &lt;!--&gt; foo --&gt;</p>\n<p>foo &lt;!-- foo---&gt;</p>\n",
---
>     "markdown": "foo <!--> foo -->\n\nfoo <!---> foo -->\n",
>     "html": "<p>foo <!--> foo --&gt;</p>\n<p>foo <!---> foo --&gt;</p>\n",

Then, we should update our own test cases and the parser if necessary.