New Feature: Add configurable HTML hook before PDF generation

[jdillard]

Adds a configuration option so users can run a custom Python script to modify the HTML (via BeautifulSoup) before PDF generation (e.g. remove, add, or change HTML elements).

Usage

# conf.py
simplepdf_html_hook = "./hooks/pdf_hook.py"

# hooks/pdf_hook.py — must define a function named html_hook
from bs4 import BeautifulSoup

def html_hook(soup, app):
    """soup: BeautifulSoup of the index HTML; app: Sphinx application. Return modified soup."""
    # e.g. remove nav, add watermark
    return soup

docs preview: https://sphinx-simplepdf--128.org.readthedocs.build/en/128/configuration.html#simplepdf-html-hook

Changes

• Added simplepdf_html_hook config option, a path to a Python script
  • The script must define a function named html_hook(soup, app) that returns a BeautifulSoup object.
• Added _load_html_hook() and _execute_html_hook() methods to the builder
• Refactored _toctree_fix() to work with BeautifulSoup objects directly (used in the same pipeline as the hook)
• Added configuration documentation and updated changelog