[AF-43] Add documentation

[ricardopacheco]

Issue number: resolves #43

Summary 🔴

We are using yard as the standard tool for documenting the entire project. Starting today with this issue, no module, class or method should be left without adequate documentation. This task is intended to add remaining documentation and improve existing documentation throughout the project.

Proposed / Possible solution 🔴

• All application code must be manually searched, and in each necessary part (module, class or method) specific documentation must be added or improved.

Checklist

• Add missing documentation;
• Improve existing documentation;
• Configure yadr server to serve documentation pages.

Additional

• In relations, use the heredoc standard to build SQL queries;