Make documentation great again.

[sleistner]

Documentation currently contains a number of dead links, which should be fixed.

[sleistner]

Documentation structure proposal:

Documentation

Introduction

• Getting Started
• Motivation
• Core Concepts
• Examples

Guides

• APIGateway Handler
• S3Event Handler
• Validation
• Error Handling

API Reference

• Handler
• ResponseBuilder
• ErrorHandler
• CORS
• Validator
• Formatter
• [Adapter]