Unhide hidden tables of contents for readthedocs (#82)

The tables of contents added to the stdlib-reference repo for use on readthedocs were not hidden on GitHub pages.
Wrapping them in HTML comments hides them, but they need to be unhidden in order for RTD to be able to use the TOCs, so this change adds a function to the RTD config file to filter out the wrapper from each doc as it gets processed.

Author: aidanfnv

docs/conf.py

@@ -8,9 +8,27 @@
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
 import os
 import sys
+import re
+
 sys.path.insert(0, os.path.abspath('.'))  # For finding _ext
 sys.path.insert(0, os.path.abspath('..'))
 
+def source_read_handler(app, docname, source):
+    content = source[0]
+    # Regex to find the comment block and extract its content
+    pattern = re.compile(r'<!-- RTD-TOC-START\s*(.*?)\s*RTD-TOC-END -->', re.DOTALL)
+    
+    def uncomment_toc(match):
+        return match.group(1) # Return only the content inside the comments
+
+    # Replace the comment block with its uncommented content
+    new_content = pattern.sub(uncomment_toc, content)
+    source[0] = new_content
+
+def setup(app):
+    # Connect the handler to the 'source-read' event
+    app.connect('source-read', source_read_handler)
+
 project = 'Slang Documentation'
 author = 'Chris Cummings, Benedikt Bitterli, Sai Bangaru, Yong Hei, Aidan Foster'
 release = '0.1.0'
@@ -76,4 +94,4 @@
 }
 
 # Use default Furo sidebar configuration - remove custom sidebar
-# html_sidebars = {}  # Let Furo use its defaults
+# html_sidebars = {}  # Let Furo use its defaults