Add comprehensive README documentation

[Victorcorcos]

Summary

This PR adds a comprehensive README.md file that transforms the project's documentation with detailed function references, usage examples, and integration guides. The new documentation provides complete coverage of the mathematical expression parser's 60+ built-in functions across multiple categories including arithmetic, trigonometric, string manipulation, matrix operations, and date/time functions.

Key Documentation Enhancements

• 🧮 Complete Function Reference - Documented all 60+ built-in functions with syntax, descriptions, and examples
• 📊 Comprehensive Tables - Organized functions into logical categories (arithmetic, trigonometric, logarithmic, string, matrix, date/time, etc.)
• 🎯 Practical Examples - Added real-world usage examples for each function category
• 🚀 Integration Guides - Included C++ and WebAssembly integration examples
• 📐 Architecture Diagrams - Visual representation of the parser's architecture using Mermaid
• 🏷️ Version History - Complete changelog from version 2.1.0 to 4.0.7
• 📜 License Information - Clear BSD-2-Clause license documentation

Technical Coverage

The documentation now covers:

• Mathematical operations (basic arithmetic, trigonometry, logarithms)
• String manipulation functions (concatenation, case conversion, substring extraction)
• Matrix and array operations (creation, manipulation, transpose)
• Date and time calculations (current date/time, differences, formatting)
• Logical and comparison operators
• Type casting and conversion functions
• Utility functions (regex, masking, parsing)

Impact

This documentation improvement makes the library significantly more accessible to developers by providing:

• Clear function syntax and usage patterns
• Comprehensive examples for each feature
• Professional presentation with badges and structured sections
• Easy navigation through categorized function tables

The README serves as both a quick reference guide and comprehensive documentation, reducing the learning curve for new users while providing detailed information for advanced use cases.