Allow structs to be used as data

[zoedsoupe]

Description
Handle struct to be used as data. Although peri doesn't support struct as schema definition yet, it
makes sense to define schemas for structs while passing the struct as data to be validated.

Related Issues
This solves #6.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• My code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

Additional Context
N/A