~jaro/balkon

ref: 32e1c8399998cc6aee135657d7616d3236197359 balkon/lib/Data/Text 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.