~jaro/balkon

ref: 22f5b8331b78ed7f4bf318a36198a6ad4dd127fd balkon/lib/Data/Text/ParagraphLayout d---------
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.