Fastback.jl documentation (especially API doc)

[femtotrader]

Hello,

Fastback.jl currently lacks comprehensive documentation that would help new users get started quickly and experienced users find detailed API information. The existing documentation provides a basic outline through examples but needs expansion to make the library more accessible.

Proposed Solution

Implement a comprehensive documentation overhaul that includes:

1. Create a full API Reference page with detailed documentation for all public functions and types
2. Restructure the Index page to be more user-focused with clear value proposition and navigation
3. Enhance the Glossary with proper cross-references to API documentation
4. Add comprehensive docstrings to all core types and functions in the source code
5. Integrate the new pages into the documentation build system

Best regards,
Femto