Docs: Improve readability of reference page (#605)

This uses some (but not all) of the settings recommended at
https://mkdocstrings.github.io/python/usage/#recommended-settings.

Changes to the "Reference" page:

- Replace section heading with function name (instead of function
  declaration): This should be more readable.
    - The function declaration is now shown in a code block instead of
      the heading.
- Added "Table of contents" to the right, to quickly navigate to a
  particular method.
- Removed "Source code": It removes clutter from the page and probably
  wasn't very useful (but it can easily be added back if needed).

Author: bbc2

mkdocs.yml

@@ -13,7 +13,14 @@ markdown_extensions:
   - mdx_truly_sane_lists
 
 plugins:
-  - mkdocstrings
+  - mkdocstrings:
+      handlers:
+        python:
+          options:
+            separate_signature: true
+            show_root_heading: true
+            show_symbol_type_heading: true
+            show_symbol_type_toc: true
   - search
 nav:
   - Home: index.md