Enforce a more strict typing programming style

[lightningspirit]

Purpose

• New feature
• New renderer
• Bug fix
• Documentation
• Refactoring
• Test Case
• Other

Description

As this library uses TypeScript, we should provide a more strict typed programming style. For instance the render function should have their own type to aid the development of external renderers.

Possible solution

Add a RenderFn type which renderers should implement.