feat: support footnotes in markdown

Author: shenxianpeng

readme_renderer/markdown.py

@@ -34,10 +34,10 @@
     from cmarkgfm.cmark import Options as cmarkgfmOptions
     variants: Dict[str, Callable[[str], str]] = {
         "GFM": lambda raw: cast(str, cmarkgfm.github_flavored_markdown_to_html(
-            raw, options=cmarkgfmOptions.CMARK_OPT_UNSAFE
+            raw, options=cmarkgfmOptions.CMARK_OPT_UNSAFE | cmarkgfmOptions.CMARK_OPT_FOOTNOTES
         )),
         "CommonMark": lambda raw: cast(str, cmarkgfm.markdown_to_html(
-            raw, options=cmarkgfmOptions.CMARK_OPT_UNSAFE
+            raw, options=cmarkgfmOptions.CMARK_OPT_UNSAFE | cmarkgfmOptions.CMARK_OPT_FOOTNOTES
         )),
     }
 except ImportError:

tests/fixtures/test_GFM_footnotes.html

@@ -0,0 +1,8 @@
+<p>a statement<sup class="footnote-ref"><a href="#fn-1" id="fnref-1" data-footnote-ref>1</a></sup></p>
+<section class="footnotes" data-footnotes>
+<ol>
+<li id="fn-1">
+<p>this is true <a href="#fnref-1" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
+</li>
+</ol>
+</section>

tests/fixtures/test_GFM_footnotes.md

@@ -0,0 +1,3 @@
+a statement[^1]
+
+[^1]: this is true