~jaro/balkon

ref: 01cd9cc6548f5469ec6a252987cdb1d40d403d28 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.