docs: Add HTML documentation generator and improve documentation structure

- Add html_docs/ directory with Python-based documentation generator
- Include custom CSS styling for modern, clean documentation layout
- Update README.md with improved formatting and documentation links
- Enhance markdown documentation across all docs/ files:
  - Improve API documentation with better code examples
  - Refactor DOCUMENTATION_INDEX.md for clearer navigation
  - Update EMBEDDING.md, CUSTOMIZATION.md, and other guides
  - Standardize formatting and improve readability throughout
- Fix inconsistent line endings and formatting issues

The HTML documentation generator creates a styled, browsable version
of the project documentation for easier reading and navigation.

html_docs/README.md

@@ -0,0 +1,34 @@
+# ReiLua Documentation
+
+Simple HTML documentation for ReiLua, inspired by the Lua manual style.
+
+## Contents
+
+- index.html - Homepage
+- manual.html - Complete user guide
+- reference.html - API reference (1924 functions and structures)
+- style.css - Stylesheet
+- generate.py - Documentation generator
+
+## Viewing
+
+Open index.html in any web browser.
+
+## Hosting
+
+Upload the entire html_docs folder to your web server.
+
+## Regenerating
+
+If you update the markdown source files, regenerate with:
+
+    cd html_docs
+    python generate.py
+
+Requires Python 3.
+
+## Style
+
+Clean white background with navy blue headers, inspired by the official Lua manual.
+
+Simple, practical, and easy to read.