~jaro/balkon

ref: 75e3b64a230f131fcde0b12604a187aef4ee2853 balkon/lib/Data d---------
Update documentation and derived instances.
Expose ParagraphConstruction.
Hide Rect union from public interface.

The function behaves in a specific way that should not be relied on by
other modules.
Use internal library to hide non-public modules.