Polish documentation and README for improved clarity and professionalism

[Copilot]

Overview

This PR significantly improves the documentation and README for the dart_either library, making it more professional, easier to understand, and better structured for new users while maintaining technical accuracy.

Changes Made

📝 README.md Enhancements

Modernized Introduction

• Transformed the introduction into a clear, bullet-pointed format with emojis for better visual appeal
• Added a concise tagline: "A lightweight, type-safe library for functional error handling and railway-oriented programming"
• Restructured the credits and support sections with horizontal separators for improved readability

Enhanced "Why Choose dart_either?" Section

• Reorganized into clear key advantages with descriptive icons:
  • 📦 Lightweight: Focused solely on Either
  • 📖 Complete Documentation: Every method documented with examples
  • 🔄 Monad Comprehensions: Full sync and async support
  • ⚡ Async Operations: Built-in Future<Either<L, R>> support
  • 🧪 Thoroughly Tested: Comprehensive test coverage
  • 🎯 Battle-Tested: Inspired by proven implementations

Improved Installation Section

• Added commands for both Dart and Flutter projects
• Better formatting with code blocks for terminal commands

Comprehensive "What is Either?" Section

• Clear definitions of Left and Right with proper formatting
• Added collapsible "Problem with Exceptions" section with real-world examples
• Expanded explanation showing:
  • Why exceptions are problematic (not tracked by compiler, no compile-time safety)
  • How Either solves these problems
  • Right-biased operations and early termination
  • Quick examples demonstrating common patterns

Enhanced Usage Guide

• Better categorization with clear descriptions:
  • Factory Constructors: Create Either instances directly
  • Static Methods: Advanced creation for complex scenarios
  • Extension Methods: Convenient conversions
• Improved code examples with detailed inline comments
• Added real-world HTTP request examples with proper error handling
• Better structured monad comprehensions section with clearer explanations

Professional References Section

• Updated with better titles ("Learn More About Functional Error Handling")
• Improved contributions section with clear calls to action

📋 CHANGELOG.md Restructure

• Adopted the industry-standard Keep a Changelog format
• Added proper semantic versioning structure with version comparison links
• Categorized changes using standard sections (Changed, Added)
• Enhanced descriptions with emojis (✨ for new features, 🎉 for major releases)
• Added comparison links at the bottom for easy navigation between versions

📚 Library Documentation Improvements

lib/dart_either.dart

• Enhanced main library documentation with clearer title
• Better structured overview section
• Improved explanation of the problem-solution paradigm
• Added "Right-biased Operations" subsection for clarity

lib/src/dart_either.dart

• Enhanced Either class documentation with professional formatting
• Clearer problem/solution structure
• Better code examples in documentation comments
• Improved explanations of core concepts

Impact

These improvements provide:

1. Better First Impressions: Professional, modern documentation that immediately conveys the library's value
2. Clearer Understanding: Enhanced explanations make the Either monad concept more accessible
3. Easier Navigation: Improved structure and organization help users find information quickly
4. Better Examples: Real-world code examples with detailed comments show practical usage
5. Industry Standards: Following Keep a Changelog and best practices improves maintainability

Testing

• All changes are documentation-only (no code changes)
• Backward compatibility maintained 100%
• Markdown formatting validated
• Links verified for correctness

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Polish docs and README</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #31

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[Copilot]

Pull Request Overview

This PR polishes and modernizes the documentation across README.md, CHANGELOG.md, and library documentation files. The changes improve readability, structure, and professionalism while maintaining backward compatibility.

Key changes:

• Enhanced README with better formatting, clear sections, and comprehensive examples
• Adopted Keep a Changelog format for CHANGELOG.md with semantic versioning
• Improved library documentation with clearer explanations and better structure

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
README.md	Modernized with emojis, visual separators, reorganized sections, expanded examples, and improved navigation
CHANGELOG.md	Adopted Keep a Changelog format with proper semantic versioning structure and comparison links
lib/dart_either.dart	Enhanced documentation with clearer section headers, better Either concept explanations, and improved examples
lib/src/dart_either.dart	Improved structure with better formatting, clearer explanations of Either concepts, and enhanced code examples

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[Copilot]

[nitpick] The removal of the period at the end of the GitHub URL in the author line breaks consistency with markdown link formatting conventions. Consider keeping the period for proper sentence structure.

Suggested change

	/// ### Author: [Petrus Nguyễn Thái Học](https://github.com/hoc081098)
	/// ### Author: [Petrus Nguyễn Thái Học](https://github.com/hoc081098).

[Copilot]

[nitpick] The empty comment lines ('///') were removed from between function declarations. While this improves readability, ensure this aligns with your project's documentation style guide for spacing between related code examples.