~jaro/balkon

ref: cebfb4e28e07f2707240abe1f4fe3cd4aeff2cc5 balkon/src/Data/Text/ParagraphLayout/Internal/Rich d---------
Expose piecewise paragraph construction.
Consolidate tree types into one.
Add ancestor boxes to interface.
Implement Rich pagination.
Implement piecewise paragraph construction.
Add basic support for Rich layout.